I’ve located multiple online posts stating different required ages. I found posts from posters in Poland stating the required minimum age is 13, 15, and 16. I don’t think I can provide any further assistance because of no formal confirmation from Apple.
It may be related to Ask to Buy settings.
If Ask to Buy isn't working - Apple Support
It may also be related to your Apple Account (formerly Apple ID) age. If your Apple Account was setup before you were 13, you will need to contact Apple Support to have your age set correctly. Your parent or guardian may need to call Apple Support to confirm your age.
Please contact official Apple Support.
Polska
00800 4411875