I think that people forget that you get smarter and more mature as you get older, but is smarter and more mature, age is not measurement of how intelligent or mature you are in comparison to other people, only to your past and future self, humans just want to have an easy maturity rater that requires no thought whatsoever. If you go kill people simply because it was in a video game, you are not an impressionable youth, you are just incredibly stupid, if you learn how to kill people through watching a movie or playing a game you are just a normal person, they don't want anyone to see things or do things that they would not want to see or do themselves current or when they were the age the person in question was. They are projecting their own fears onto someone else, and to these people I say: "GET A FREAKING LIFE!". But that's just my extremely long and poorly thought out theory.