I'd say 15 cos the fact that he still lives with his parents means that he is not old enough to leave home yet. Or at least leave home with his parent's permission. So yeah. 15 years old.
I'm guessing about 16. Given Rev's appearance, demeanor, and his menial delivery job, I'm thinking it's very reasonable that he probably is only 17-18 himself. Actually, on that subject, it's not at all unlikely that Tech may be the oldest loonatic (although Slam's another possibility).
Personally, because I believe Rev to be 18 himself, I like to think that Rip is 15. *shrugs*
And, also, he seems to be going through serious identity issues... like a young boy going through puberty... *shrugs*
And, like Akira said, he still lives with his parents... With his apparent disapproval of the way they treat him, you'd think that he'd have moved out if he could...
Just me though...
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Andrea: ....I think my kidney laughed. Sye: Your bladder told it to stop. 83