Xbox LIVE allows gamers to create an online identity and compete alongside millions of others in multiplayer games. When setting up an Xbox LIVE account, users must create a "gamertag," choose a membership, and enter some personal information for their profile--including date of birth. If you entered that information incorrectly, or if you wish to change it for whatever reason, you can log into the Windows LIVE website (which lets you manage your profile across all of your Microsoft accounts).
Navigate to the Windows LIVE home page (see the References section for a link).
Click the "Sign in" link in the upper-right-hand corner of the page.
Enter the e-mail address and password associated with your Windows LIVE ID (this is the account you created when you signed up for Xbox LIVE). Sign into the account, which will bring you to your profile page.
Scroll to the bottom of the webpage and click "Account" in the lower right-hand corner.
Click "Registered Information."
Change your date of birth and click "Save."