See European age verification app to keep children safe online and https://ageverification.dev/
The EU Age Verification Solution relies on Zero-Knowledge Proof (ZKP) cryptography to deliver its privacy guarantees. A ZKP allows the user’s application to convince a relying party of a single fact — for example, “this user is over 18” — without revealing the user’s identity, date of birth, issuer-assigned reference or any other attribute. The application’s responses to different relying parties cannot be correlated, so a user cannot be tracked across services, and the relying party cannot build a profile from repeated interactions.