Paradoxically this is one of those features/requirements that i feel should be on the end-user-device with zero knowledge proof. It would make sense to have the enduser verification ondevice with a simple reply to any online property : Passed age verification/or not. Otherwise the centralization and eventual leak of this data is a can of worms in waiting.
EU implementation of age verification is actually base don zero knowledge proofs https://ageverification.dev/
Currently, it does not implement ZKP, and further requires proprietary Google Play Integrity use, making it an absolute toxic cesspool.