I don't think there is an age specified but seeing how Pharm is a Fresher, he's about 18/19/20, while Dean, a 3rd year student, should be around 22/23. Manow and Team, having started uni the same time as Pharm, should be around the same age while Win should be Dean's age. In Episode 17 we saw the funeral, so we know for a fact that Intouch was 19 when he died and Korn, even though we didn't see his obituary, I assume was a few years older - just like Dean. No idea about the rest of the characters, sorry