I bolded the part that I think is the central pillar of the debate that arose here. Kids fuck around because they're curious and intrigued at all of the new shit their body can do and all of the cool shit they can do to other people's bodies. There's no denying that. It really is on parents and proper authoritative figures (health teachers for example) to educate effectively and help kids understand physical facts about their anatomy that, in most cases, they are undeniably going to use. They either are informed ahead of time (prevention), or get into situations they never even considered or thought possible.
If a boy and girl were only taught abstinence, but followed their instincts anyway and ended up pregnant, with a UTI, etc. the blame is far from theirs alone, IMO.
If a girl and boy know about the many forms of birth control and healthy sexual habits such as urinating (in the toilet) after sex, and choose to ignore these things, then the blame becomes mostly, if not all of theirs.
I do not agree that a young girl (or boy, especially) is mature enough or mentally developed enough at the age of 16 to properly assess the ramifications of something like selling his or her body for sex, medical practices, etc. Science shows that our brain is developing until at least age 21.
Ultimately, I think a lot of this circles back to the idea of whether or not we should make laws to protect us from ourselves. I use those terms referring to humans in general and what we've learned about our development, function, instincts, etc.
The reason I don't support something like prostitution taking place among that age group is the same reason that hospitals make sure parents are the ones signing off on any medical decisions regarding a minor: I don't think said minors can fully process the decision that they are making in such a climate.
I tend to agree with
@David. in that prostitution should be up to the individual selling their body, but I don't trust a child to make that decision for his or her self. The other issue with prostitution is that many of those women are being forced by the trade into doing something they have no desire to do. Now, would allowing it as a legal practice fix some of that? Maybe. That's a different discussion.
When we starting doing things for the first time, we have to process what we're doing, who we're doing it with, and all of the things that come with it. That can be sex, that can be playing a sport, that can be a new job, you name it.
Asking someone, in a position like what I described above, to then make a decision about doing something like as a profession adds an entirely new layer of process that the individual likely isn't ready for. On top of that, we're talking about human beings without fully developed brains to use to make said decision.