I have had my account for years. I am not sure, but I theorise that when I created my account, I did not enter a birth date. As a result, xbox seems to believe that I am underage.
I am in fact 21 years old (I turned 21 less than a month ago). I have no option to promote my account when I go to account management, as described on this page. http://support.microsoft.com/kb/945418
Please help me.