I’m unsure what aspect of your access is being blocked, where.
Websites can have their own age restrictions and mechanisms implemented, entirely unrelated to an Apple device, or Apple Account.
Some networks will block network access entirely, and you will need to discuss that with the ISP or with regulators.
Screen Time can be used to control activities: Use Screen Time on your iPhone or iPad - Apple Support
Reset Screen Time passcode: If you forgot your Screen Time passcode - Apple Support
If you somehow have a device with Screen Time enabled by a different Apple Account, you’ll need that account, or a discussion with Apple Support.
An Apple Account has an associated date of birth: Update the birth date associated with your Apple Account - Apple Support
Edit: If you’re being asked to send proof to Facebook, that has nothing to do with Apple and Apple devices.