I don't think there is any real correlation here. Since there's no way to measure one's predilection to having sex earlier than a peer of the same age group, it's really difficult to say if one has anything to do with the other.
Sexual beings are sexual beings, it doesn't matter if they were introduced to the concept at six, sixteen, or sixty-six. If it's something they are interested in, they will find a way to earn the knowledge.
I ultimately think it's really just that simple. If a twelve year old girl is curious about sex and desires to find out everything she can on the subject, she will; regardless of the walls others try to put up for her. If a twelve year old girl isn't interested in finding out what sex is about, then she will wait until she is interested.
I think hypersexual activity seen in teenagers is something that would be there regardless if they were exposed to the world or kept in a plastic bubble with no outside information of the world whatsoever. Knowledge is just the gateway to sating their desires.