Will gamestop buy an M game if you are younger than 17

I believe that the question meant the question as asked. He wanted to trade in games to GameStop and was concerned they would not accept Mature rated games from someone underage. I believe they will if they want the game. I was planning on giving GTA for trade and was not concerned about it. But certain clerks may not accept the games based on the rating and thinking that if I am not allowed to sell it to you how can I buy it.

I don't know if the questioner meant to say "sell" instead of "buy", but it seems that "sell" was intended. Whether they care or not, you should care. Its a problem in ethics, morality, and parental control. Violating little things leads to complacency and violation of bigger and bigger things. There is a reason behind the ratings.