[Handsome Creepy Eel]

Probably a bit earlier than 18, like 15 or so seems natural. But given the devastating effect of amassing sexual partners on a woman's sexual market value, I think culture should encourage this to be later, like at least 18, maybe 20. Not all biological facts are good for us. I'm talking only about female age of losing virginity here because female preferences usually determine the frequency of sex for everyone else, unless you live a culture with very widespread rape.

This will of course never happen, but one can dream.