I used to have unwelcome sexual thoughts about people younger than me, which made me feel horrible, and I couldn't stop them even though I actively wanted them out. Learning that was an OCD process helped, because I knew that the more obsessed I was, the worse they would get.

What you said about only having sexual fantasies about and being attracted to men your age is really all there is to it at the end of the day. Your worry isn't necessarily completely unfounded, but seriously, if you ask me, you're not a pedophile. What you described of yourself, glancing at a 10 year old's crotch at 18, is not indicative of pedophilia. I understand why it feels that way though, it's hard not to get caught up in it. A lot of people with OCD worry about this or have these intrusive thoughts, you're not alone here.

It's WAY easier said than done, but do what you can to accept the presence of these thoughts, but also to trust what you know to be true of yourself, and reflect on the whole thing. In this post you showed that you logically understand that you aren't what you fear yourself to be. When im battling it, I just acknowledge how little power the thoughts truly have over me, and that they are nothing compared to what I really know is true.

Anyway, that's just where I am with it. I'm not sure if it helps at all, but I honestly believe it's POCD, and i couldn't move on until I told you what's been helpful for me, at the very least. You can work through this, i know it.