Should i just nail her?

So I'm in my thirties and decided to go back to college. In one of my classes I met this really odd girl, she's basically like that nerdy girl from high school that had no friends but there's more to it. Shes really odd, always making really off topic comments about the material outloud, in the middle of class and what not, she off handedly told me she was in special Ed classes in Highschool whatever that means.

I've become friends with her as she is incapable of dealing with the course work, so I help her a lot, I also am the type to make friends with anyone as I try not to be judgmental. By the way, she just turned 20.

Here's the thing, Im not sure why, but I really want to sleep with her, and I'm sure if I put out the effort, shed go for it. Problem is I kinda feel like I'd be robbing the craddle, and I'm not really looking to get into sort of relationship out of it.

So, what should I do Internet? Is this normal?