leave it alone friend.

take my word on this as a similar situation happened to me & it ended up horribly. (for a while it was very good though) i met a very hot young girl (she was the little sister of a girl who i was friends with, they were from a wealthy family & i was from a working class family so i was fascinated by the way they lived)
anyways i gave in to temptation & took the younger sister's virginity & started hanging out at their house. it went great for a year or so but then i realized (as you most likely will) that we were on very different levels in maturity & intellect. i'm sure, unless you are a very immature and stunted person you will want to do things that she's not ready for or can't (like anal sex or going to a bar)

so my advice is just look for a girl more your age & let the young girl go...