How to change child account age without access to organiser account

Hello Peregrine Taylor

Because the child’s date of birth was entered on the account by mistake, Microsoft may now be treating the account as a child account, which can prevent the date of birth from being changed directly from that account

In this situation, the birth date usually has to be corrected using the adult Microsoft account that originally gave parental consent. If the account shows “Parent or guardian consent is required,” a new consent flow can be started with an adult Microsoft account and then Edit this child’s personal info can be used.

Who is the organizer of your family group? Can you get in contact with them to change your date of birth?

If they no longer have access to that organizer/adult account, the best next step is to try to recover that account first, because only the adult that originally granted consent can normally manage those details.

I hope this information help, feel free reply back to this post if you need further assistance, I'll be happy to help.