Here's the average member age of the five New York families - taken from a sample provided by the family lists over on the Real Deal forum.
Genovese Family - 72 years
Gambino Family - 68 years
Colombo Family - 65 years
Lucchese Family - 64 years
Bonanno Family - 61 years
Obviously there are members both older and younger but the general range seems to be early 60's to early 70's. Probably quite a few younger ones (relatively speaking by mob standards) that haven't been identified yet.
As far as the average age a guy gets made? To be made in your 20's or even 30's is usually considered very young. I'd say it happens more often in a guy's 40's or 50's.