There’s a cultural value in virginity in girls. It’s pretty common across cultures: for marriage, virgin women are more desirable than non-virgins. It’s biased; the virginity only increases value for girls, and it probably stems from men wanting to be sure than any prodigy are actually theirs. Women can be nearly 100% sure a kid they have is theirs (not quite 100%, as there’s a brief period when a channeling swap could conceivably be made), but the men can never be certain. The best odds you have is to get yourself a virgin. So female virginity has been valued through history (by men), and I think this is where the fetish of having sex with virgins comes from.
That’s what I’m taking about. I’ve never understood the appeal of “being a girl’s/boy’s first.”