Unable to update date of birth in Apple Account

I got an iPod and therefore an Apple ID when I was 7 for Christmas. My DOB on my Apple ID says 23rd December 2016 and has always said I am 7 years olds, and had never aged up. I am now 14 and it has still never updated, saying I am 7 and I cannot edit it to my real age, as it would no longer be a child account and the help websites are not helpful. They just tell me I cannot change my age to be over 13, but I am over 13 and it is not a fault on mine nor my parents part for this incorrect age, it is that it has never updated in Apple systems. I need my age to be actually representative for app downloads and to edit payment methods so I can have subscriptions. How can I change this to my real DOB? I know I can’t change it to over 13 as its no longer a child account but I am over 13 and it is a fault in Apple systems that this is incorrectly represented.

[Re-Titled by Moderator]