I'm not going to sit here and pretend that I read through the 19 pages of comments in this thread, 'cause I didn't. I am however going to shamelessly give my take on this question, which may or may not have already been given by somepony else.
Applejack: "Ah, shoot. I was just a little filly. Even littler than 'yall"
Alright, so this obviously tells ut that "Flashbackjack" was younger than the present day CMC, including Apple Bloom. But wait, speaking of Apple Bloom, where is she? When young Applejack leaves the farm, she is nowhere to be seen, and neither are the parents that would be neccesary for her to be born later. In my mind, the logical conclution here would be that Apple Bloom has already been born, and is simply too young to be present with the family. I'd say a year, possibly younger.
This means that the timespan between the story and the present is roughly the same as Apple Bloom's age. Give or take a year, we get this approximate: AJ-AB<AB, or AJ<2AB
Now in English that would mean that Applejack is rougly Twice Apple Bloom's age possibly a year or two younger than that, depending on how much younger than Apple Bloom "young Applejack" looks.
If Apple Bloom is 10-13 years old, for example, Applejack would be 18-25. This is what makes the most sense to me in the context of the show and the characters. I realize of course that this does not conflict with the already established concencus of the forum, but it's always nice to have some hard facts to back this stuff up.
Besides, using the established math, I can conclude that Spike and the CMC is roughly the same age, as his birth is in fact shown in the flashback itself.
As for the others... I'd say Fluttershy is the oldest, at about the same age as Big Mac. This is purely based on them being about the same size in the flashback. My opinion on age does not really differ from others' but: Fluttershy(23)>Pinkie(22)>Applejack(22)>Rarity(21)>Twilight(20)>Rainbow Dash(19)