Cant use facebook entered wrong dob on setup - Microsoft Xbox 360 Arcade

Okay, since an Xbox live account takes it's information from Windows Live, this is what you have to do:

Go to Hotmail.com
Sign in using your Xbox Live account e-mail and password

If you're not already signed up for mail, don't worry about it. Click view contacts if you're not already signed up.

In the top right corner click options
click More options
Click View and Edit Your Personal Information
Click Registered Information
Change your birthdate
click Save

Your age is changed!
This may or may not be enough

If it is: HURRAY! If not: read on

Sign on to your xbox 360
Open the guide menu
Go over to System setup
Go to Account Information
Click Promote Child Account
It will ask if you want to connect to Xbox Live
It will then take you to the account setup
Click continue
Then You will need to enter Credit card information. It is supposed to be a new one.
You need to accept a new terms of use then follow the prompts.
Next it will bring you back to the dashboard (you will be signed out) Sign in, accept the terms of use again, and you're all set. Have fun!