Keep in mind that Bastila is a "young padawan"..I don't think she's in her late or even her mid 20's...I always imagined her being like 20-22ish, and Revan in his mid or late 20's. Carth is probably around the same age as (maybe a couple of years older, since he is his superior at the beginning of the game) Revan...Mission is obviously like a very young teenager....don't know enough about Wookie lifespan (not THAT into SW haha :P) to tell you anything like that.
But even though Bastila in-game looks very old, I always imagined her being A LOT younger, just because I'm 99% sure that along the game somewhere a lot of people describe Bastila as a "young padawan". Take into consideration that Anakin was like 18 or something when he started truly becoming Obi-Wan's padawan and no longer a childish apprentice and think about how despite everyone saying Bastila is incredibly powerful, if she's in her late 20's, then she's been a padawan for 10 YEARS. I mean I don't know if that's a normal wait time (whatwith the jedi preaching patience, haha :P) but to me that sounds like a very long time, especially considering everyone tooting her horn.