Heck... I don't let my 8yo play all the ***E*** games out there...
But I DO let him play several Teen or Mature games. (Halo series, & Assassins Creed series)
It's one reason why I get an "approved" list from parents before playdates ("Hey... if the xbox comes on, are there time limits you'd like / which -if any- games would be okay?" We have a pretty decent range; from kinnect dance to lego to first person shooter). I just teach my son that different families have different rules, and we go by the lowest common denominator. Ditto, when he's at friends houses. Some of his friends aren't allowed to play Halo, but are allowed to play World at War (which he isn't). So neither game (theoretically) gets played. In all reality, not ALL of kiddo's friends' families check with us, but most do.
I personally take Teen to = Parental Guidance (although I do 'parental guidance' with E games, as well), and M games to = (not without explicit parental approval).
What bothers me more is the whole peer pressure/ ganging up on YOU that your friends and family did. What's right for one child, even in the same sibling group, isn't necessarilly right for all... MUCH LESS in different families.