Normally, statutory rape laws recognize age differences between
partners. This keeps 19-year-old men from getting convicted of
statutory rape in engaging in consensual sex with their 17-year-old
girlfriend after the prom. It also recognizes that there's a difference
between an eighth-grader experimenting sexually with a sixth-grader,
and his (or her) doing the same with a third-grader. It works pretty
well.

I interpret those virginity statistics differently: most teen-age
girls have the one and only thing required to persuade a member of
the opposite sex to deflower them in the social convention: a vagina.

Boys, on the other hand seem to have a higher bar set for them
by the pool of potential partners. Those that do succeed in
becoming sexually active, however, tend to enjoy the same success
with multiple partners, over time. Older boys, as they proceed
through secondary school, are able to be successful with and
interested in the girls in the lower grades. It's much more rare
for an older girl to have any interest in a younger boy.

The result isn't too different from seal rookeries--- there are
a smaller number of successful males servicing a population of
available females.