If the age verification is going to mandate government issued ID, the government issuer can be the Trust Anchor issuing a Digitally Signed Credential for the zero knowledge proof - using any available open source zero-knowledge process:

1) zkcreds-rs (zk-creds) [1]

2) zkLogin (Sui Foundation) [2]

3) TLSNotary [3]

4) DECO (Chainlink/Cornell) [4]

5) Anon-Aadhaar [5]

[1] https://github.com/rozbb/zkcreds-rs

[2] https://github.com/mystenlabs/sui/tree/main/sdk/zklogin

[3] https://github.com/tlsnotary/tlsn

[4] https://chain.link/education/zero-knowledge-proof-zkp#preser...

[5] https://github.com/anon-aadhaar/anon-aadhaar