hmmmm interesting. Is that only because of insecurity when dating more experienced people or other reasons too?
99% of it is.
Some girls get all panicky when they are 20+ and date a guy who is 20+ and the guy has clearly had sex many times and the girl is still a virgin. Or for that matter, I know a situation where that's reversed (guy is virgin, girl is not) They get scared that their partner will expect sex and dump him or her if he or she wont put out. They get scared that when they do try to have sex with their partner they won't get it right, or they will be bad in bed. etc etc etc.
Personally, I don't consider myself a complete prick... but if I go out with a girl my age for a month and shes STILL not putting out then she'd have to be REAL special for me to stick with her any longer than that.