The problem isn't the girl--it's the girl's dad. She might be DTF, but if her dad hears about it, you can bet he's not going to say "oh, it's just a two-year difference...that's totally cool!" He's going to be seeing you as the pervert who raped his innocent little girl. And he'll find someone who's happy to listen and act at the local police department.
When I was on the board of the local junior football/cheer program, we performed background checks on every prospective coach and board member. You'd be surprised at how many people we had to turn away because they turned out to be registered sex offenders for just the kinds of things you are considering doing now. These are people in their 40s and 50s. They will carry that legal stigma forever, and all of that information is usually just a Google search away.