At the same time, ignoring the fact that their bodies are telling them certain things (and causing them in their immaturity to act on it from time to time) is a mindless pursuit, and what's even worse is deeming them slutty because of it.
People are people, with different hormones, drives, likes and dislikes, and scowling at a 14 year old who acts on it is ineffective.
You have hit the nail directly on the head.
However, the trend is continuing: Drinking ages have been raised to 21. Drivers licenses are held back 'till 17. Marriage ages in many states has been pushed back. Furthermore, 14 and 15 yr olds have been handed a world of sophistication, but are expected to tread water until they reach a legal age or accomplish a certain academic level.
On another front, this man made construct is also a result of parents who are unable to let go of their "babies". The same parents that do everything but teach their children to be self capable and self responsible.
Actually, if these girls parents would 'scowl' a bit at sexual immorality instead of just going about with the attitude 'Well, they're going to do it anyway,' these girls might have a bit more self-control.