500 Kegs of Headcannon.

See Here.
The following resides 1/4 written down and 3/4 in my head. Continued sanity after reading not guaranteed.

The Princesses:

Q-1 How old are Celestia and Luna?
A-1 For simplicities sake, lets say that the MLP:FiM universe is half as old as our own.
A-1.1 Metaphysically speaking, Celestia & Luna, along with 6 other aspects, are literally as old as the concepts/objects they maintain/control. In this order they are older than Discord. Assuming that their universe actually revolves around their planet (Equuis) then; Time > Death > Sun > Earth > Moon > Water > Plants > Animals > Chaos.
A-1.2 Physically speaking, Celestia & Luna, along with the 6 other aspects, are much younger. They don't bother taking physical form till after Discord beings his reign of chaos. They take form in the order of escalation of Discord's actions: Chaos > Plants > Animals > Water > Earth > Moon > Sun > Time > Death.
A-1.3 So either close to half as old as our universe or somewhere between 7,000 - 10,000 years, (depends on how you look at it).

Q-2 How old is Cadance?
A-2 Seeing as I have her as the second of two daughter between Nightmare Moon and King Sombra, born on the moon about a month after NMM is banished there, puts her at about 1,002 years old. (This is more or less ripped right from a fic where the foal doesn't survive because no air.)

Q-3 Were Celestia and Luna always alicorns, or did they ascend?
A-3 Ah, easy one. They've always been alicorns in the sense that, that is the form they first chose when they entered the physical plane.

Q-4 Are Cadance and Twilight immortal?
A-4 Yes.

Q-5 Have there been other alicorns in the past?
A-5 Aside from the other aspects? 3. Who also happen to still be around.

Q-6 How much authority do Celestia and Luna have in Equestria?
A-6 As much as they want so long as the reason they have said authority doesn't weigh too much on their conscience. (They know more than you do most of the time. They have more experience in general than any one pony. They could kill you easily, in many ways. They were given the job.) They do delegate a lot of simple/repetitive bureaucratic work to councils and the like so that they have time to themselves.

Q-7 Does Shining Armor rule The Crystal Empire along side of Cadance?
A-7 He does because Cadance wouldn't have it any other way.

Q-8 Other than Twilight, Luna, and Cadance, what relationships have been important to Celestia in her lifetime (students, close friends, lovers, family)?
A-8 The 6 other aspects I've mentioned earlier. Discord. Various OCs of my own creation that will go unnamed because spoilers. Starswirl the Bearded.

Ponies and Equestrian Culture:

Q-9 Are there still cultural differences between earth ponies, pegasi, and unicorns, or is the culture homogeneous by the time shown in canon? Are there cultural stereotypes (positive or negative)?
A-9 I'm gonna go with Tundara's answer for this one because I've never really put that much thought into this.

Q-10 Are there foods or items native to Cloudsdale that are uncommon on the ground? Are there foods or items on the ground that are uncommon in Cloudsdale?
A-10 Yes. Ditto just about any/every other village/town/city.

Q-11 Can all unicorns learn all spells, given the time and effort spent practicing them, or is magical talent usually limited in some way?
A-11 Potentially any unicorn could learn any spell. Those spells relating to their cutie marks are easier to learn than those that aren't. The only other limiting factors are how much magic a spell needs, how much control is required, and whether or not the caster believes the spell works.

Q-12 Earth pony magic: Does it exist? What is it?
A-12 Yes. Mostly its Strength and Stamina. Ridiculously good at growing food most of the time. And if they lack any of those, they usually end up with some sort of metaphysical ability. (Pinkie Pie has two for example, her 'Pinkie Sense' (ability to predict the future), and cartoon physics.) Discord thought Earth Ponies were too boring so he decided to make them a bit more interesting.

Q-13 Some pony families we’ve seen seem to have naming conventions (the Apples, Twilight’s family) and others don’t appear to (Rarity’s family, Pinkie’s family), which is more common? Are there reasons for one or the other?
A-13 Going to quote my buddy ultra1437 for this one.

Q-14 How much formal schooling is an average, middle class pony expected to complete?
A-14 I see ponies starting school at age 4 or older. Age 3 if the parents want to send them to Preschool. (There is no Kindergarten, that would be preschool or 1st grade.) Something like 4-6 years. Usually by this time they've gained their cutie mark and focus on learning what helps them fulfill their special talent. Collages and Universities do exist, but those are usually for the most driven of ponies.

Q-15 What’s the average lifespan for a pony? At what age is a pony expected to be independent of their parents?
A-15 Easily 90 years. Pegasi tend to average about 75 because of their lifestyle. Its not uncommon for Earth Ponies to reach 100, something usually gets them before then. Unicorns vary widely depending on their magic. Some blow themselves up young, others have so much magic they can live to be 300 some years old, so long as they keep control of it.

Q-16 Are there roughly an equal number of male and female ponies?
A-16 Somewhere between 2-1 and 3-2, female-male.

Q-17 How informed are most ponies about things that happen in other parts of Equestria? What about other parts of the world?
A-17 About the same as any random person on earth. Also depends on Era and place of residence.

The Main Characters:

Q-18 How old are the Mane Six? Spike? The CMC?
A-18 As of Season 1, Episode 1:
---CMC - All of them are 6 years old,
---Spike - 7
---Twilight Sparkle / Rainbow Dash / Pinkie Pie - 17
---Rarity / Fluttershy / Applejack - 18

Q-19 Did Fluttershy remain on the ground after getting her cutie mark? Were she and Rainbow Dash friends all along, or did they drift apart for a while?
A-19 She went back to Cloudsdale long enough to finish flight school, but otherwise stayed on the ground. Shy and Dash stayed friends, that's why Dash moved to Ponyville.

Q-20 Rarity and Applejack both seem to have grown up in Ponyville. What were their interactions like before the show?
A-20 They knew each other about as well as anyone would in a small town. Didn't really socialize outside of public events though.

Q-21 What do Twilight and Spike consider their relationship to be?
A-21 Their relationship evolves over time. Though at any one time it could revert depending on circumstances. Mother/Son > Sister/Brother > Best Friends.

Q-22 When did Pinkie move in with the Cakes? Is she a worker who rents a room, an apprentice, or is there some other relationship?
A-22 Shortly after gaining their cutie marks, Pinkie & Rarity pump into each other on Pinkie's family farm. To make sure Rarity got home safely with the gems she bought, (at a discount price since she and Pinkie both just got their marks), Pinkie and her family escort Rarity home. On their way out of town, they stop by Sugarcube Corner, which captures Pinkie's attention. A few years later after graduating from 6 years of school, (Pinkie ain't no dummy), she see's about getting a part-time job at Sugarcube Corner. Eventually moves in and her rent is covered by her pay.

Q-23 Who among the Mane Six had the best parents growing up? The worst parents?
A-23 Oh boy, here we go. Twilight's parents, as well as her brother, sitter, and teacher are all super supportive, (they all just wish she would get out a bit more). Pinkie's parents are about average. Big Mac, AJ, and Applebloom's parents are dead, because I'm a bit of a dick, (not quite sure on what killed them though). Fluttershy has three sets of parents, the details of which would be major spoilers. Rainbow Dash's parents are supportive. Rarity's parents stayed home more round about till Sweetie Belle was 4 years old.

Q-24 Why didn’t the CMC hang out more/know each other before Call of the Cutie?
A-24 Quoting my buddy ultra1437 here again.

Q-25 Is Scootaloo an orphan? Will she ever be able to fly?
A-25 Yes, my Equestia is not always sunshine and rainbows. Yes, I'm not that evil.

Q-26 Will Apple Bloom’s cutie mark involve an apple in some way, even if it’s unrelated to farming or baking?
A-26 Probably.

Q-27 How is Sweetie Belle’s relationship with their parents different than Rarity’s was?
A-27 Sweetie Belle knows who her parents are, but sees them more as the awesome aunt/uncle that come by every now and then.

Side and Background Characters:

Q-28 Is Mr. Cake the father of the Cake twins or not?
A-28 Yes.

Q-29 Are Big Mac and Cheerilee an item, romantically?
A-29 Friends. Possibly had sex once. Otherwise no.

Q-30 How did Prince Blueblood get his title?
A-30 He's the latest in a long line. The first few of which would love nothing better than to teach the seemingly arrogant prick a few lessons about how a worthy noble should act.

Q-31 Is Silver Spoon equally as bad as Diamond Tiara?
A-31 On a scale of 1 - 10, DT is 10, SS is 7.

Q-32 Is Zecora’s magic common among zebras?
A-32 Zecora is a high level shaman, but not the highest. She has been trained by the best though.

Q-33 Why does Daring Do publish her stories as fiction?
A-33 Some wouldn't believe her and others would freak out too much.

Q-34 Do you have a strong headcanon for any non-speaking or one line background ponies that you want to share?
A-34 Lyra is actually a Sea Pony and one of many offspring of the Aspect of Water. Bon Bon is one of Chrysalis' daughters that got sick of the Hive life and left, (her pony disguise is of her own making, she doesn't imitate any pony in particular). Vinyl Scratch is the daughter of Hoity Toity & Photo Finish, her sister is Sapphire Shores, and she's a vampire. Octavia's parents are Unicorns, immensely proud of her musical talents, but displeased that she is an Earth Pony, (she also ends up as a werepony, (werewolf watever)).

Other Species:

Q-35 Does Equestria differentiate between speaking and non-speaking species, in terms of respect, rights and legal responsibilities? Is there some other line or scale used? (For example, how are cows classified? Diamond Dogs? A chimera?)
A-35 ultra1437 hits the nail on the head again.

Q-36 Do other speaking species form their own nations, or are all nations largely integrated, with some having larger populations of a species than others?
A-36 Each speaking species have at least a form of government. A nation? Depends. The Buffalo are nomadic. The Zebra tribal. And the Dragon's have their 'strongest dragon's word is law' methodology.

Q-37 Are minotaurs related to cows at all?
A-37 Discord.

Q-38 Do all zebras rhyme?
A-38 The older the zebra, the more they rhyme.

Q-39 Do zebra cutie marks work the same way as pony cutie marks?
A-39 More or less.

Q-40 Do any species have types of magic, other than ponies and zebras?
A-40 Each species' magic depends on what part of their body is made of Alicorn, (extremely magic conductive material). Alicorns - entire body. Unicorns - skull/horn. Pegasi - wings. Diamond Dogs - arms. Zebras - blood. Dragons - scales. Donkeys - bones/muscles. Earth Ponies - entire body, save brain, (not stupid). Changelings - carapace. Minotaur - bones/muscles. Griffins - beak/eyes/claws/wings/paws. Buffalo - entire body, save brain, more their blood though. Cows - digestive organs, (their milk is like 10 times more nutritious than any other species' milk).

Q-41 Is the lack of buffalo presence in Equestria cultural, or simply because most pony towns aren’t built to accommodate a full grown buffalo?
A-41 They're nomadic. They don't stay in one place long enough for it to matter.

Headcanon and You:

Q-42 Do you consider official sources other than the show (comics, card game text, movies, novels, etc.) to be canon?
A-42 Depends on my mood.

Q-43 Do you have one headcanon that you always use, or do you switch depending on projects?
A-43 One extremely convoluted headcanon is enough to keep track of thank you.

Q-44 Can you easily accept the headcanons of different writers? Do you prefer when stories match your headcanon?
A-44 Easily enough yes. Not really but it doesn't hurt.

Q-45 Is there a part of your headcanon that you wish was more popular among writers?
A-45 All of it.

Q-46 Is there a popular piece of headcanon that other writers use that you dislike?
A-47 Haven't found it yet.

Q-47 Have you ever written a story or blogpost just to explain some part of your headcanon (other than this one)?
A-47 Not yet.

Q-48 Does your headcanon influence things like your favorite pony, ship, or episode?
A-48 A little.

Q-49 Would it bother you if the show proved part of your headcanon wrong? Any specific piece that would really bother you to lose?
A-49 Nope. Just another challenge.

Q-50 Is there something that wasn't asked about here, but you feel like you need to explain to everyone?
A-50 Perception is reality. Think about that for a while.

Comments

[Drifting Heart]

Your headcanon is pretty cool.