Are they considered Immortal, or do they just have an extended lifespan?

Might seem a silly question, but I don't really know and would like to for my next fic

That's up to you. In a lot of fics, they're immortal, and in others they're just long-lived. Whichever works for you.

1059927
My headcanon is that Alicorns are immortal.
But Cadence and Twilight aren't.
Reason I say this is because we saw Cadence growing up naturally in the canon show. (That flashback)
Since I can only assume that Cadence had ascended to Alicorn form from Celestia or Luna, it's safe to say that Twilight will only grow up normally.

1059927 None of the above. They're whatever works for you.

1059932
Also there was a statement from one of the show's staff that Twilight would not outlive her friends.

1059927
I've always liked the idea that they CAN live forever, but are susceptible to lethal things like disease, physical damage, etc.

1059927 They do not age, but they can be killed is one of the more popular fanons. I believe Faust's original idea was that they aren't immortal, but with other people running the show now... who knows. Either way, you can write it however you want.

1059936
I remember that. I believe it was McCarthy's?

If it's just my opinion on it It'll be able to work, thanks for the replies guys :D

1059927
The answer about alicorns is always No. I haven't even seen the question yet

EDIT: Ok, after read the question, I think alicorns just can use aging spells because they are the higher unicorns that Twilight meant in Magic Duel episode.

On a side note. Why Alicons with capital A? we dont capitalize Dogs,every time, Or race factions for the matter.

1059936 From which you can infer either that she'll live a normal lifespan, or that they're also going to live forever.

1059955
The first of which hopefully being the case, although the second being more likely to actually happen in the show (I'd assume they wouldn't show the mane 6 dying in the show, probably.)

As far as life spans are concerned, its just a case of whatever works for you. Make them immortal, have very long life spans, or just can perform age spells on themselves, it is all the same in the end.

1059953 I think for a while alicorn was capitalised as it is considered part of a proper title - short for Alicorn Princess, but yea, it doesn't need to be a capital every time.

FIRE THE HEAD CANON:
There are two types of alicorns.
TRUE Alicorns, like Celestia and Luna, they are the equivalent of Greek Gods, powerful, immortal, flawed
and
NEW Alicorns, like Twilight and Cadence, they are the equivalent of Greek Demigods, powerful, mortal, a little more interesting in the original story.
I mean come on...
Show of hands how many of you know the story of Heracles/Hercules and how many know the story of Zeus, or of Hera.
Throughout the course of history there could have been many ponies who "ascended" (is the word I use) into alicornhood and died of old age (or killed off)
But wait there is more:
If you consider true alicorns being part of all three types of ponies (earth, pegasi, unicorn)
And new alicorns of only two (their original type + another)
ie. Cadence pegasus+unicorn
Twilight unicorn+pegasus
then...
wait for it...
Doctor Whooves at one point will become an alicorn!
earth pony+pegasus

And no, that is not an pegasus pony that looks like him, I choose the more epic answer. Because:

1060084
BUCK YEAH! ALICORN PRINCE THE DOCTOR!

1059936
Considering they said they will never tackle the issue of death in the show, that means nothing

1060138
Like I said in my second comment. That means that either the issue will never be addressed in the show or that the rest of the mane six will become alicorns.

1059999
Princess doesn't need to be capilalized either, or any title, just when it followed by a name. "Whatever that Princess Celestia does to look so young after 1000 years, should be the envy of any other princess."

1060193

the rest of the mane six will become alicorns.

I'm going to kill you Garbo.