How to make my parents let me get a Sims game?

Just sit them down and talk to them about this, say that the sims 3 isn't going to have any in it if it is aimed at people who are 12+, and say to them that you are 13 and your not a kid anymore, say that, your friends are allowed games like that and just tell them that you know about the 'facts of life'. If you are mature and calm about it hopefully they will hear you out, because it is unfair that they are treating you like a little kid at your age, tell them you want to be treated more maturely and open up to them and tell them how you fell. good luck.