Your Xbox Live account is managed by Microsoft and you can log into your Live.com account at any time to change your personal settings, including age. For now, it is not possible to enter new information directly from an Xbox console, so you will need to change it through the website.
Steps
Step 1. Connect to the official Microsoft Live site at login.live.com
Step 2. Enter the login credentials of your Xbox Live account and click on "Sign in"
Step 3. Click on “Your info” on the left in the blue bar at the top, then on “Edit your personal info”
Step 4. Go to the appropriate drop-down menu to enter the day, month and year of birth
Step 5. Enter the new date of birth, then click on “Save”
Your age will be updated for all Microsoft accounts linked to the one you just changed, including Xbox Live.
