alt Hacker NewsZero-knowledge seems to be a bit of an oversell here. It is more like you break the knowledge up and only share the relevant parts with each party. And the facilitator (Google) arguably has access to the most information out of any of the parties involved.
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There are true ZKP setups where no one learns anything but the absolute minimum (e.g. is this person over 16, not what is their dob). This is hard to prove though and I don't know if I trust Google to do it
Ideally the government would be the issuer and the facilitator but the US lacks the state capacity to do this. Maybe it will work that way in Estonia.
Google has pioneered a few technologies where they are the trusted dealer. For example, Private State Tokens.
I have written a paper on how to do age verification in a completely privacy-preserving way, and it doesn’t even need zero-knowledge proofs:
zero-knowledge proofs are a well-known tool in cryptography [1]. All Google is sharing is the library to implement it. Google would not have access to the information any more than they have access to the bank info of people who use Android or Gmail.
[1] https://en.wikipedia.org/wiki/Zero-knowledge_proof