My parents would already freak out because of the relationship with three persons in it. Guess you got lucky. I don't know if I would like it if it was my daughter. 10 years age difference is nothing to sneeze at. I'm 26 now and I already consider 19-year-olds pretty much kids.
In two years it will suddenly suddenly acceptable for her to drink alcohol (assuming you're in the USA). Hard age limits are always weird but still helpful.