There was a post on Ponychan that I thought really adresses the issue of their ages well. I can't remember it verbatim, but I remember the age estimations:
Pinkie Pie and Twilight: 17-18
Rainbow Dash and Fluttershy: 18-19
Rarity and Applejack: 20-21
This has been my head-canon ever since I read the post.
Twilight appears to be college age, and all six either live on their own or are at least out from under parents.
Eh, my headcanon for their ages is:
Rainbow Dash + Applejack + Pinkie Pie: 18
Fluttershy's confirmed to be a year older than Pinkie Pie. Twilight is still studying, though at what level we don't know (probably college level or older). Applejack helps out/works on the farm and runs stalls, so I'mma assume she's older than 16, because that's the minimum age for working in most countries (though idk, Equestria could be very different). Rainbow Dash and Pinkie Pie are a shot in the dark. Fluttershy lives alone without her family or parents, so she's probably one of the older of the group. Same with Rarity, Rarity runs her own business so I assume she's the oldest.
/my headcanon sucks.
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I'm guessing Pinkie Pie is the youngest. She certainly seems like it. I also agree that Rarity and Fluttershy are probably the oldest. The others, I'm not sure.
My Little Pony: Friendship is Magic provides a realistic representation of life in Ponyville - YouTube
There's an Anti-Brony named Bronanthedestroyer who I've been arguing about his "opinion" of "Bronies being the scum of the Earth" in the video's comments. It's been going on for a week and I've just about had it. His head is so far up his @$$ that it's astounding. Go to the comment section and press (show the comment) for each of my replies and his replies to get the full scope of things. I probably shouldn't do this since I'm likely going to land myself in hot water with the mods (I must look like a bullied kid who's crying to his friends for help) and it IS Youtube but I've got to get this off my chest and show this pompous jackass to others like you. He really redefines the meaning of "Anti-Bronies." And hey, it IS relevant to the topic.
See the comments first.
Youtube is full of idiots and trolls, so of course anti-bronies will be that realm, along with Gen I purists. Remember to not feed those parasprites again.
I read somewhere that the Mane Six are supposed to be physically young adults, but mentally a little younger than that, fwiw.
After watching the newly released "Meet the Pyro" trailer, it struck me the idea that someone should make a Pyro music video with Pinkie Pie's Smile song, because they're always paired up together in Gmod videos and how they have similar personality traits. They've already made a Skyrim music video for the song, so why not TF2?
Haters gota hate
Applejack: OK, this is just gettin' weird. Real me! Real me!
Anyone seen the .MOV series? Pinkie Pie's video is already out today, so that leaves only Rainbow Dash for the last video: SWAG.MOV