There's a poll on another site about this:

http://male101.com/faqs/pn/virginity.html

Actually that site has all kind of interesting anonymous polls about male sexuality and male mastrubation. Some responses are obviously fake but most of it does appear to be pretty genuine.

I love reading that "caught mastrubating" survey. Pretty interesting IMO.

Edit: Looks like they have a female version of that site now too with the same polls:

http://female101.com/faqs/pn/virginity.html