Re cultural variation, I don't think it's so much that indulging in what your hormones tell you is learned behaviour; I think it's more the other way round: restraining yourself from following your hormones is learned behaviour. Or more often than not, behaviour imposed by others.
Most cultures have some kind of norm for regulating sexual behaviour, usually very different for men and women, often class-bound, but almost always transgressed by some.
In cultures where the chastity of women is highly prized, young people tend to be guarded very closely and not allowed to be alone together once they reach puberty, which rather suggests that people do not believe they would only have sex if actively encouraged to do so.
In some societies (e.g. rural w/c areas of northern Europe in the 19th century), there might be a tacit understanding that young people do have sex but as long as pregnancy results in marriage, this is not a problem. Indeed, knowing for a fact that your bride is fertile might be a definite asset in a farming community where strong arms are needed.
In the same locality at the same time, the young lady of the manor will be watched like a hawk, because her pregnancy would have a totally different impact on the people around her. In the meantime, some kindly cousin might well be taking her brothers to the brothel to further their education and give them an outlet for their sexual urges.
But most societies seem to think that "young folks will do it if they come to it" (apologies to WS for gender-neutral misquote).