True, though as a girl's "purity" became more and more prized as a character trait (ie, from the 1800's on), the lower classes also tended to have sex earlier.

I really only know what I'm talking about in Victorian times, but while the girls of upper standing tended to marry in their very late teens-early twenties and treated sex as the Ultimate Big Deal, the common working women would often lose their virginity far earlier and engage in casual sex in a way more on par with what we consider "normal" behavior today.

So basically, when people rail about the loss of morals and the dissolution of society vis-a-vis sexual behavior, what they're really railing against is the fact that we have recently rejected aristocratic social structures, and are more and more adopting those of lower classes in the past.

Maybe if I write this now, while drunk, you'll all understand.