This may vary, but the information that I found was "under 11".
Child is considered 3 to 11, adult is 12+, to see rated R movies you have to be 17+, and someone that is 21 or older can purchase rated R tickets for people under 17 if they are attending the same movie.
To buy a rated R ticket or for the cheaper kids tickets. For the kids tickets it's usually under 11 or 12. To buy a rated R ticket it's usually 17 or 18. But to buy someone else a rated are ticket who is under age is 21. Hope that helps.
18 yrs under that is a student
18 years old
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