Let us see, I believe he was going to be trained, or had already started training, as a Jedi when the enclave was destroyed, and I would guess that he was between ten and fifteen when that occurred. I do not think that a distinct time was ever mentioned in relation to the gab between the first and second games, but if it was ten to twenty years that would make Mical anywhere from twenty to thirty-five.
Edit: I would guess that Atton is between thirty and forty, and the "kid" remark was a direct reference to Han Solo's nickname for Luke.