It might be inapropriet for people under 17 so the might need adult supervision, according to the american rating system. But if you are talking about the canadian rating system, anyone under 18 must have an adult guardian nearby.
Because it is considered that only after the age of 18 a person attains enough of wisdom to think it's good and bad own-self, as R rated movies are not good for anyone.
I think 13 would be the best age to watch an R rated movie.
Because they might need a guardian or something like that lets use friday the 13 as a example ok it has sex not for kids people.
Well I watch rated "r" movies and shows and I'm under eighteeninfact I love themyou get to see nudityloljokes