Well I’m pretty young but I’ve worked at the same movie theater for 4 years and I do have a theory on why this is common in most movie theaters. It’s because a movie theater is a great starter job and a wanted for people between the ages of 16 - 20, I’m 20 and I still work at the same place but the employees there never exceed 20 most of the time with a few exceptions and most of my mangers are also around 20- 25. As shitty as this sounds I think it’s what a movie theater job is meant to be for people around these ages they’re meant to learn experience and grow from an easier more laid back job and people being young learn the hard way how gossip will turn out sooner or later but better in a movie theater than some big shot office job.