There are younger VC & MC winners out there!!
Seems old enough to command a platoon under fire in Iraq or Afghanistan so I would think that the slightly less pressured job of flying an airliner should be within the grasp of anyone in their early 20s (caveatted of course with the personal maturity of the individual)
There are many 40+ year old pilots I have flown with who I only get into the cockpit with out of sheer curiosity. Age tends to bring greater experience but the individual personality you have may make you 20 years older or younger easily!! Good luck VT