This passage will guide how to retrieve your parental email address. If you just forget the password, you may reset the password.
I have posted on Microsoft Answers, Xbox Forum, contacted with online agent and even make a call to Xbox. (Thanks they understand my Asian English) No one can solve it. Then, I have a solution.
First, you need to go to this page where says parental approval required. You need to enter parental email address and password. The problem is that you or your parents forget the email address.