How old should a kid be to be allowed to play the sims 2?

In your opinion how old should a child be to play the sims 2/sims 3? I have a sister who is 9, and has the sims castaway and pets.... those are the only ones because no one thinks its a good idea for her to be able to make people make out/woohoo/fool around etc. I agree with them because she isn't very mature about anything (giggles at body parts/kissing uality etc) and tends to say awkward things that should not be said in public... What are your thoughts? Is there a way to disable certain things in the sims games for ps2?