If you have a child account that is not attached to a family account, you can’t make changes to or access your Xbox profile settings.
For example, you can’t view or update the following if you have a child account that is not attached to a family account:
Profile (including your gamertag)
Xbox breaks the definition of a child account into three categories:
Young child: Anyone under the age of 8
Child: Ages 8 through 12
Teen: Ages 13 through 17 (or 19 in South Korea)
In this scenario, you must have a parent or other adult in the family add you to the family account on the console before you can make changes to or access your Xbox profile settings.
Before a parent or adult can add you to the family account, they must have an Xbox profile. If the parent or adult does not have an Xbox profile on the console, go to one of the following pages to learn how to add an Xbox profile to the console:
If you only need to change your gamertag, you can make the change on the Xbox app on Windows 10. To do this, go to the “Change your gamertag in the Xbox app on Windows 10” section of the How to change your Xbox gamertag page.