I, at 30, am the youngest player in a group where most are in their mid-30's. I started back in the mid-80's with the Red Box (precocious little scamp that I was), and played pretty much every edition up until now.
I'm guessing the actual numbers will be skewed towards an older, 25-and-up demographic as the core audience for 4th. A lot of players born after 1990 or so likely gravitate more towards MMO's than pen-and-paper RPG's simply out of convenience and familiarity, leaving the average age to climb steadily as time goes on.