How old do you think the main six would be in human years?

I think they would be around the same age. Fluttershy is a little older than the rest.
Mentally I think Pinkie would be the least mature; say between 12 and 18 in human years.
The most mature pony would be Twilight, mentally 18-22 in human years.
They are all independent and at least half of them provide for themselves, but on the other hand they have a lot to learn, so I'd say they are young adults, mentally in the 17-22 years range in human years.

Ok well in on of the episodes flutter said she was a year older then pinkie so my guess would be: Rd about 17 18ish rarity about 20is pinkie 15 fluttershy 16 twilight 19 18ish AJ about the same age as twi or rarity just saying

Sorry but really the ponies dont have much of an age if you ask me. They don't have sexual orientations but age... i thin Lauren Faust said they were around their 20's or so.

Twilight: Late teens
AJ: Mid to late teens
Pinkie Pie: Early to mid teens
Fluttershy: Early teens
RD: Mid to late teens
Rarity: Late teens to early 20's In my opinion, anyway.

Twilight:19
Rarity: 17 1/2
Rainbow Dash: 18
Applejack: 17 3/4
Pinkie Pie: 15
Fluttershy: 16 (My age!)

I'm going to say that the mane six are anywhere from the ages of 18-22. Here's a link to an cool article talking about this: question:link

I think
-Rainbow: 15
-Twilight: 16
-Rarity: 17
-Fluttershy: 16
-Pinkie: 15
-Applejack: 18

Twilight: 19-21
Pinkie: 16
Rarity: 18-19
Applejack 18
Rainbow Dash: late 17- 18
Fluttershy: same as Dash

ALL:13

Dash: 14
Twilight: 15-16
Rarity: 20-22
Fluttershy- 11-12
Pinkie- 10-11
Applejack- 15

Rainbow Dash: 16 or 17
Twilight Sparkle: maybe 19 or 20
Rarity: 21
Fluttershy: 16
Applejack: 17
Pinkie Pie: 15

Twilight: 15
Rainbow Dash: 14
FlutterShy: 14
Pinkie Pie: 13
AppleJack: 16
Rarity:16

Well, according to My Little Dashie, one human year equals one day in Equestria, sooo... :I

Twilight- 17
Fluttershy-19
Pinkie Pie- 18
Apple Jack -18
Rarity- 18
Rainbow Dash- 18

Twilight-17 or 18 AJ- 18 or 19 RD-18 Flutter-16 (in a episode she claimed shes older then Pinkie) Pinkie-14 or 15 Rarity-19 i hope this helped u ^-^

Here's what I think
Rainbow dash: 15
Apple Jack: 18
Pinkie pie: 14
Twilight: 119-20
Fluttershy: 15
Rarity: 16

Pinkie - 18-20
Rainbow Dash - 18-21
Fluttershy - 19-23
Applejack - 20-24
Twilight Sparkle - 23-25
Rarity - 26

This is just my theory.
Apple's family reunion is held every 8.3 ( "100 moons" ) years. AppleJack was a baby at one of them. This means that at least some of them are 8, 17, 25 or 30. As Sweetie's nightmare in For Whom The Sweetie Belle Boils showed, Rarity was already adult when Sweetie Belle was 5. Sweetie Belle is meant to be a young child, 8-12 most likely. If she is 8, she was 5 3 years ago, which means that Rarity cannot be 8 or 17. So, she is about 25-30. I doubt that they are 30, so i will settle down for 25. AppleJack and Fluttershy were in their class to get cutie mark while Rainbow Dash was first. Other 3 are somewhere in-between. So, AppleJack and Fluttershy are 25, Twilight, Pinkie Pie and Rarity are 24 and Rainbow Dash is 23.
But hey, that's just a theory. A GAME THEORY.

I think rainbow dash is 18
Fluttershy 19
Pinky pie 18
Twilight 18
Applejack 19
Rarety 19