When you set up your profile you probably stated that you were under 17 at the time. I guess Microsoft is enforcing the age limit to play the newer games on Xbox LIVE.

When I created my profile, I just changed my birthdate so I wouldn't have to deal with parental content and such. You can't change this so you are either going to have to create a new account, or use your parents e-mail address and have them approve it.

These e-mail addresses should have been entered when you created your account.