I think that part of why we go to theatres is the shared experience of a movie. It can make a good movie great. Oohs, ahhs, squeals of delight or horror - it's part of the immersive environment, to know that other people are reacting emotionally to the content beside you.
What detracts from a movie is an audience (young or old) acting as if the movie is secondary to whatever else they are doing.
I like to think I added to someone's experience of the movie Predator (the remake, with Adrian Brody). I was watching intently, and at a particularly startling scene, let out a yelp and tossed my popcorn bag into the air, showering the people in front of me with (fortunately unbuttered) popcorn. I was mortified and apologized in whispers; they thought it was hysterical, as did the rest of the group with me and a few other patrons who saw what happened. I'd never done that before, and never since.
I had a friend talk me into going to see Aliens. Against my better judgment.
Afterwards, she said she would never go to a scary movie with me, because the way I kept jumping when things happened in the movie was far worse than the movie itself.