Theaters aren’t mandated to check for ID. The R rating is determined by the Motion Picture Association of America, which is not a federal agency. It is a non-government organization. Therefore, theaters are only obligated and not mandated to check for ID. The worst they can do is deny you; the best is allow you in. This varies from theater to theater. If you’re 18, you’re above the 17 age restriction for R-rated movies. And even though the R rating says R movies are inappropriate for children, I saw an R-rated movie with one of my parents when I was in middle school.
I agree with Calvin. I hated gym class and liked academics more.