How to change age of an account of a Member of My family? Can Apple correct this

This is primarily a user-to-user support forum; other Apple users like you. See the following from Update the birth date associated with your Apple ID - Apple Support

If you need to change the birth date for a child, contact Apple Support. 

Click on the blue links in my previous reply for instructions. If the current birthdate is for someone under 13, you can't change it -- you can only contact Apple Support as described in my previous rreply.

See information in Update the birth date associated with your Apple ID - Apple Support