As I learn more about AS, I've been reading that Aspies are less likely than NT's to be fazed by age. For example I read about one 21-year old Aspie who was frequently cruel and violent to his girlfriend. His girlfriend was 71.
Indeed some of the ladies I have my eye on are much older than me, though nowhere near as old as 71.
Be that as it may, I would never ever recommend getting into a relationship with, or dating, an underage girl. Thinking of you and your integrity more than anything.
Please don't be tempted by this girl's interest. It just isn't worth the risk, and the risk drastically outweighs the value of any relationship with her (think of how people are going to see you, and their reactions).