*Treads carefully, hoping that this isn't even vaguely thought of as underage sex talk - which is definitely NOT the intention*

I suspect that it's far more common than many may think:

As a child, many a time I would play games which could be considered of a sexual nature - and know this is normal behaviour. From the "show me yours and I'll show you mine" through "doctors and nurses" (AKA grope session, but didn't know it was called that then) to things like "cops and robbers" (with clothing penalties, of course); and for the latter if there'd been a pair of handcuffs available I'm certain they would've been used. And possibly the only thing stopping me tying the girl next door naked to a tree in the garden as a "captured squaw" would have been that "Mummy will get cross". Obviously I would have had thoughts about these bsdm-ish activities. If any of my friends had mentioned sexuality though, I wouldn't have know what they were talking about.

I think the only thing maybe unusual in your case is that (if I read your post currectly) you realised that such thoughts were sexual - which also implies that you were taught or found out very young what sex actually is (and you haven't mentioned any experience of child-abuse, for example, which may explain how you knew about sex). You mention a "catalyst" - I'm sorry, but didn't understand that bit - but that may be the missing link...

Also, I know that psychology teaches that we are all predisposed towards sex, even from a very very young age. I'm not quite sure what you mean by physiologically predisposed?

So I'm sorry to say it, but you are quite normal - at least in my humble opinion!

VV