Lee Fletcher - 14
This isn't canon. I don't know Lee's birthday or canon age, so I'm going to make him a bit older than Aster. If this is wrong, please correct me; it is just because he's the head of the Apollo cabin. He'll be a bit older.
Michael Yew - 12
Aster Ray - 11/12 (was born in the same year as Percy, just at a later date than the story takes place.)
Percy Jackson - 12
Annabeth Chase - 12
Grover Underwood - 28 - 16 (biologically)
Will solace - 10.
Luke Castellan - 19 (I think)
Clarisse La Rue - 15
I'm not sure if these are 100% canon or not, please correct me on this matter.