And a good way to ensure that you stay out of trouble with the law is to not have sexual contact with a child. Period.
Aside from sexual offense charges, there are others that could come into play, such as contributing to the delinquency of a minor. As PA's entire code isn't online and what IS online is out of date, it's very difficult to find out what all legal issues you could be facing.
Here's an idea. Go ask her parents if it's okay if you have sex with their daughter. Their reaction
should knock any thoughts of lust for the girl out of your head.