How old are the ponies?

[Tom Gallagher 33,521]

Rarity and Applejack are definitely the oldest. For the others I don't really know. It's never really clarified apart from Fluttershy saying she's a year older than Pinkie early on. 

I always thought of Fluttershy as being slightly older. I'm going to assume Pinkie is the youngest and Twilight, Rainbow Dash and Fluttershy are somewhere inbetween. 

[Splashee 28,537]

I'd say 12 years old. 13 is an odd age, they start growing body parts, you know? 13 would make them all look like Luna  

[Rushing cash 824]

Lets see, FS is 1 year older than pinkie according to her. The M6 got their CM at the same time, RD was first(or at least pretty early) in her class to get one while AJ was the last, so according to it AJ is probably older than dash. FS in the flashback appears slightly older than RD, maybe she just developed faster but its reasonable to assume she is older than RD a bit too. Based on this, I believe its: FS> or = AJ > PP > RD. Rarity seems like older than dash, and its really impossible to place her accurately in it(rarity too TBH). And, RD participated in the young fliers competition, so I guess she is probably 16-18 at that point, maybe around 20 at most, they all finished school(how schools even work in equestria?) expect twilight but she is celestias student so it doesn't apply here.

My guess, is that from youngest M6(RD: 16-20) option to oldest M6(AJ: 20-22) option is 16-22 years old(in human years) in season 1. In my opinion: AJ> R> FS> TS> PP> RD. 

I think SG is actually older than the M6, by a couple of years. The crusaders were 6-8 in the first season.

[Landi 597]

I think they are young adults around their early-twenties. They are mostly independent and even have their own jobs. Plus they have the adult pony body shape.

Now for ranking them based on age it's difficult. All we know for sure is that Fluttershy is a year older than pinkie. My guess is that Rarity is the oldest followed by Applejack, and that Pinkie is the youngest. Now, I still am not sure on the order of the middle three. Although, Rainbow said she was one of the youngest in her flight class, so I can assume that she's younger than Fluttershy (who was also in her flight class). I'm still unsure about the age of Twilight, though.