Our local PCA is has a spread of ages... but probably 70% are over 40. As far as skill level goes, it's the older guys that have dedicated race cars, and aggressively pursue racing. No autocross for them... they do club road races at Robling Road (Savannah, GA), Charlotte Motor Speedway, Daytona, etc. 130+ mph on the straights racing. These old guys can teach you a thing or three.
When you young guys see an older guy, all you see is the snow on the roof. Believe me, there's still a fire burning in the fireplace for most of them/us.
I'm 45, and I used to think that was old. Now I'm thinking 65 or so is getting old...