I'm 21 and haven't lost it yet.
I flat out refuse to go to a prostitute even if I get desperate-reason being, I want someone to sleep with me because they want to, and are attracted to me, not because they need extra money for heroin or whatnot.
I'm kind of running out of chances now though-until I get a job I don't get many opportunities to go out and meet girls, and even then I'm not the best at "chatting up"
I'm the sort of guy that girls grow to like, rather than immediately think "Wow, he's gorgeous!"