Turn off my age restriction

Try this

1. Open the Settings app.
2. Tap Screen Time, then tap Content & Privacy Restrictions.
3. Enter your Screen Time passcode if requested.
4. Tap App Store, Media, Web & Games (or Content Restrictions).

Change options like Apps to Allow All or Web Content to Unrestricted. 

If you are in the UK, the following may apply:

Age requirements for managing an Apple Account in the UK – Apple Support (UK)

If you’re asked to confirm that you’re an adult – Apple Support (UK)