Change my birthday date

Click on the link to read how to 'Update the birth date associated with your Apple ID' - https://support.apple.com/HT204164

- "Be sure to enter your correct date of birth. After you change it to any age below 13, you can't edit it."

For a child under 13 you will have to contact Apple:

Click here --> https://support.apple.com/choose-country-region/ Select your country, then a product and work your way down the menu until you reach the help you need. If you do not find it, select a different topic and work you way down to any option that results in a telephone or chat request.

Contact Apple for support and service - "See a list of Apple phone numbers around the world." - https://support.apple.com/HT201232

There appears to be a conflict in opinion over the space of about 24 hours among Apple as to whether or not Apple's own documentation contains a recommended solution for changing the age on an Apple account. --> how do I change me age? - Apple Community

Hello and thank you for using Apple Discussions.

You can view the full official instructions regarding your question by clicking on this link: Update the birth date associated with your Apple ID - Apple Support

If you have any further questions do not hesitate to ask.

Thanks.

1. Open Settings
2. Click your name at the top of the list
3. Click Name, Phone Numbers, Email
4. Click on your birthday to change it

Of course the Recommended solution only helps you if your are using an Apple mobile device and haven't accidentally set your age below 13. I strongly recommend you read Apple's own documentation about how to do this.