Rated M for mature, though.
What I used to do when my parents would determine which games I got was this:
Explain to them that you're old enough to deal with it in a mature manner and that regardless of if you get the game or not you will be exposed to it one day. I would always bring up the fact when it came to nudity/brief nudity/sixual themes that if that was really all that I cared about in the game then I would just go get on the internet and not spend $60 on computer generated images. Or when it came to violence, it was better to experience it on TV and in games than to get too curious one day and wonder what a person would look like when they've been decapitated.
After a while your parents will begin to trust you being around things of that nature because they know you'll handle it maturely. For instance I turn 17 in February, but my parents have been ok with me watching R rated movies with very explicit content and playing games with explicit content since I was about 13, even younger when it came to movies (Watched "Platoon" when I was 7). Just explain to them that they can trust you to be mature about it.
Oh and once you gain their trust do NOT do anything to lose it. I've been there, done that, and can say that when you have just about every privilege taken away from you that you took for granted, your life will become a very dull and monotonous one.