I suspect the age range of the Mane 6 is quite large. Rarity being the successful owner of a growing business would indicate the equivalent to at least human mid-20’s, when you account for education and generating the capital for getting the business going. I tried to estimate her age assuming Equestrian ages translate directly to human ages and came out with a range of 31-35, given the age of her sister. I’m going to assuming there is some Cutie Mark magic somehow expediting the training aspects, and that pony ages don’t directly map to human ages, and thus split the difference and say late-20’s for her. At the other end of the scale, Twilight at the start of the series seems to be the equivalent of straight-out-of-college (or perhaps straight-out-of-grad-school). Given her nature, it’s wouldn’t surprise me if she was the Equestrian equivalent of someone who got skipped ahead at school, started college young, and graduated early. I suspect she’s the pony equivalent of only just old enough to drink.
Assuming Rarity is the oldest (if anyone was older than our estimated age range for her, things would start to become even less consistent than they already are), Twilight is the youngest thus far considered, and Fluttershy and Rainbow Dash are about the same age (i.e. close enough to attend Summer Flight Camp together) we get something approximating relative ages for five of the Mane Six:
- Rarity
- Fluttershy, Rainbow Dash
- Pinkie Pie, Twighlight
How to differentiate ages between Fluttershy and Rainbow Dash? I can think of only one line of reasoning. In ‘The Cutie Mark Chronicles’ Fluttershy has taller, leaner look than most fillies, which suggests maybe she’s undergoing the final growth spurt to adult size (I have no idea about growth patterns in real horses, BTW), whereas Dash is still rather… compact. So let’s say that Flutters is slightly older than Dash, but Dash is still older than Pinkie.
What about Pinkie and Twilight? Without going into too much detail (and there is a lot to go into, trying to establish relative ages for Shining Armor, Maud, and Limestone), I believe Pinkie is probably a little older, given that she seems to have an established career in Ponyville. This gives us…
- Rarity
- Fluttershy
- Rainbow Dash
- Pinkie Pie
- Twilight
So what about Applejack? This is where, if you consider the detail, you can easily wind up with dissertation-sized texts considering the relative ages of all Mane Six siblings, Spike, Cadance, Gilda, Cheerilee, etc., etc., etc.. I’m just going to go with this: in ‘The Cutie Mark Chronicles,’ Big Mac seems to be undergoing roughly the same growth pattern as Fluttershy (i.e. lanky), so I’m going to assume that they’re around the same age, which would necessarily put AJ at the younger end of the herd. Given her propensity for being concerned and motherly about other characters, I’m going to arbitrarily slot her in between Twilight and Pinkie. So, to summarize my over convoluted headcanon, the ages of the Mane Six are something like this, with approximate ages in parentheses:
- Rarity (28)
- Fluttershy (26)
- Rainbow Dash (26)
- Pinkie Pie (25)
- Applejack (23)
- Twilight Sparkle (21)
tl;dr version: I think the Mane Six are all in their twenties, ranging from 21-28