You don't mention the gender of the 16 year olds, but last time we were there in March, we experienced a handful of college-aged girls on the beach that were not shy about their bodies (read: topless). It didn't bother us much, but we just had our 6 yo (at the time) daughter with us.
As for things to do, one activity we have enjoyed (and would be fun w/ 16 year olds) would be to go to the Lucky Strike bowling center. If you haven't been to one, it is a really cool place w/ music, video walls, etc., targeted to the younger crowd.
Kurt