I am 18, so yes, I would say a 15/16 y.o girl is likely to be fairly naive compared to me... and in my experience, they are. JayB124 made a very good point about the booze... youngish girlies do tend to drink more than they can take and get very silly. But then again, so do some blokes.
But in general, its not age at issue, it is maturity. My bf is 25 years older than me, he accepts me as an equal because I am not silly and naive, and because I have intelligence and judgement. I know plenty of women close to his age that act like teenagers....