It depends on the movies rating.
I would say at least 13 and older without being questioned where your parents are. I was dropped off all of the time as a kid. For "R" rated movies you have to be 18 or older and that's for a single ticket by yourself. You can not purchase "R" rated tickets for anyone else unless you're 21 and over and must sit through the entire movie with those you purchased the ticket for. ID is required for both.
18 or older
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