Xbox Live account did not become adult.

You have to leave the family.

Hello there!

Regarding your question, please try to go on your Microsoft account information and make sure that the date of birth indicates that your age is no longer a minor.

Once you do that, just follow the steps on this link in order to remove your account from being a child on the Microsoft family it has been added to Xbox Support.

You can later on add it but this time as an adult not a child.

Heya!

Unfortunately, there is no way to alter an accounts age that would make the account become an adult account.

The account will automatically become an adult account once it has reached the appropriate age for your country/region.

In this situation we recommend having the adult account
check the privacy options for your account and ensure that you have an
Xbox Live Gold subscription as it is required to play online.

We hope this help explain why you are unable to play online!

The adult account need to upgrade to adult or wait until the child account becomes adult in prder to change it...

The "adultness" of an account is determined by the birthdate you entered when you created the account.

Only if your account is at the age of legal maturity in your country, your account automatically becomes an adult account.

While you can set your account to have "adult" settings like allowing you to talk to everyone on Xbox Live or play Mature or Adult Oriented games, this still does not unlock the feature of changing your gamer picture.

That is only possible on "real" adult accounts that reached legal adult age according to the accounts birthdate.

And no, you can't change the birthdate afterwards.