Account Age

The age of the account is determined by what was put in when the account was created, not the age of the Microsoft account. You'll have to wait until the age of the account turns 18. There is no way to change the age.

That's for age verification for using a Microsoft account. Changing the age of a Microsoft account does not change the age of an Xbox account.

The age is set by what you enter when you create the account, not by the age on the Microsoft account. So changing Microsoft accounts will not change the age of the account.

no once set the age of an account can't be changed till the account turns 18

Changing the age nor the email of the account affects the Xbox accounts age

It's not possible to change the age if an Xbox account. The age is set by what you put in when you created your account, not the age on your Microsoft account. You will have to wait until the age of the account reaches 18.