Age of the Mane 6 & Spike

Based on the assumption that the events in The Cutie Mark Chronicles occurred about 11 years before the pilot, the age of the characters at the time of the pilot
Apple Jack In Apple Family Reunion they show some of AJ's baby pictures from a previous reunion. In the pilot, there are a bunch of Apples at Sweet Apple Acres. In Apple Buck Season, AJ describes this as an Apple family reunion. In Apple Family Reunion, Granny Smith tells Apple Bloom
1) There are family reunions every 100 moons
2) Reunions are always at Sweet Apple Acres
3 This is Apple Bloom's 1st reunion
I don't see any way they can both be right. I'll go with "Granny was right" because Apple Bloom was in the pilot & was old enough she would have remembered. So, this gathering was not an official reunion. AJ made a lot of mistakes in Apple Buck Season, including forgetting the sixe of her orchard. This is another mistake.

IMO, Apple Bloom was 11-12 years old during the pilot. This means there was a reunion when she was 3-4 years old. Either she was absent from the farm & missed the reunion or Granny got a little muddled & forgot Apple Bloom's exact age & Bloom was so young at the time that she forgot

So, assuming this was 3 reunions ago (25 years), she was 26 during Apple Family Reunion, 25 during the pilot, & 14 (& just graduated 8th grade & completed her schooling) when she went to Manehatten.

Dash She would have joined the Wonderbolts her 1st chance. So, the episode Wonderbolts Academy was shortly after her 18th birthday. This makes her 17 during the pilot & 6 when she was "the 1st in my class to get my Cutie Mark"

Fluttershy She was in Flight Camp with Dash. IMO, since some of the other foals had Cutie Marks she was older than Dash. But, if she was too much older, she wouldn't have become friends with Dash. So, 7-8 at the time & 18-19 during the pilot.

Pinkie Fluttershy tells Pinkie "I'm a year older than you" So, Pinkie was 6-7 when she got her Cutie Mark. If you assume she is a little older than Dash, then that makes her 18 & Flutterrshy 19 during the pilot.

Rarity The hardest to judge. She was in school 11 years ago, so 14 or younger. She graduated, went to Manehatten to learn to be a fashionista, returned to Ponyville & had her own business. But, she hasn't accomplished much yet. I'll go with 20ish.

Spike He hatched during the Rainboom, so he was 11 during the pilot. IMO, he is about 1 year younger than Apple Bloom.

Twilight She was applying to Celestia's school. Depending on whether this was kindergarten or 1st grade, she was 4-6 years old at this time. (She would have been 2-4 years old when she 1st saw Celestia raise the sun. Probably 1 of her earliest memories). This would make her 15-17 during the pilot. She was still in school. This would have been High School. It's possible she is the only 1 of the Mane 6 to go to High School.