I'd say, being that this is all fiction:

Mac - 32 (I doubt he aged as a cyborg or when he was in space)
Walter - 30
Heather - 27
Puck - 90
Marrina - 21
Snowbird - doesn't count, but 35.
Shaman - 45
Northstar/Aurora - 27
Talisman - 22
Feedback - 21
Many others would still be teens