over 21 but account is still child

changing the birthdate after account creation doesn't work

It only goes by the birthdate you put in originally

Changing the ms account doesn't affect the birthdate either

You will just have to wait for father time

Once a child account is created it will only be able to become an adult account when the child turns 18 or 21, depending on your country.

Yeah, it's still a child account. There is a parental account attached to it. Almost everything I was able to move over to my current account, so I control almost everything. But there are still disadvantages to having a child account, of course. But yes,
it's still a child account.

^ not everyone wants to lose all the stuff from their account.

To promote a child account to an adult account

Sign in to Xbox LIVE by using the account that you want to change.

Go to My Xbox, and then select your profile.

Select Manage Account.

Select Promote Child Account.

Note This option is available only if the date of birth for the account indicates that you have reached the age of adulthood (18 in the United States). The legal adult age varies by country and region. The age of an account owner is calculated by using the
date of birth provided when the account was created. This date cannot be changed. If you entered an incorrect date of birth when you created the account, your only option is to create a new account using the correct date of birth.

Follow the on-screen instructions to promote the account.