Here are everyone's official ages--first their ages in FFIV, and then, for your convenience, with seventeen years added.
PHP Code:
Cecil   - 20 - 37
Cain    - 21 - 38
Rosa    - 19 - 36
Gilbert - 24 - 41
Yang    - 35 - 52
Porom   -  5 - 22
Palom   -  5 - 22
Cid     - 54 - 71
Edge    - 26 - 43 
Lydia is seven at first, but there's no account for exactly how much she aged by the time she returned from the World of Phantom Beasts. And considering she goes back to stay there at the end of the game, there's no telling what age she should be in The After. (Like I said before, she should really be dead.)