Only rated R
Only if the movie is rate R than they need an adult old than 21 years old to be with them. But anything under that rating would be ok. My brother and his friends (all 16 years old) when to see the Incredibles 2 with no problem on Friday and they weren't harassed by anyone
I've seen teenagers without any adults at the movies, I believe it should be ok if the movie they are watching doesnt require adult supervision.
It all depends on the family and their rules for 16+
Thanks! Your answer is awaiting moderation.