All Movies have ratings. You could watch an R18 movie and be 7 years old. Most parents would not like that at all, but lots of people do watch movies that they shouldn't and think it's awesome. It's not.
I know tonnes of kids that do watch movies they shouldn't and it changes the way they act and it's always bad. Best case scenario they would start swearing, worst case scenario they don't talk at all. I think the reason lots of kids do it is because they think that other people will think they are cool but in reality it changes them... a lot.