I was talking to Alvin Fielder once and mentioned "the young drummer Mike Reed." Alvin's response was something like "he's in his thirties at least, so he's an old guy now!" and proceeded to ask whether there were any real young (under 23) drummers making a splash, and I actually couldn't think of any.
Yes, Mike is in his mid-30s, but of very worthwhile drummers I know and get to hear a good deal, Marc Riordan (also an excellent pianist) is 29, and Dylan Ryan is 27. Other notable youngish players I'm aware of are altoist Nick Mazzarella (27), trumpeter Jaimie Branch (27) and Brooklyn-based trumpeter Jacob Wick (26).
Indeed on some of these names. I always think of 20s-30s as "young" but to some I guess it isn't.