alt Hacker NewsZero knowledge proof is either trivially defeated by re-using the same credentials or doesn't have useful privacy guarantees. There really isn't an in-between here for something like age verification.
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It's funny because the same "perfect is the enemy of good" argument is used both to criticize age verification in the first place (why bother if it isn't perfect) but then also to dismiss proprosals to implement it better (why bother if they don't perfectly fix the problem).
Age verification in general is not intended to defend against people lying or using stolen credentials. If you’re 13 but know the password to your dead grandpa’s account and the website in question has no idea he’s dead, there’s no way to defend against that, with or without a ZKP.
What the ZKP does is let you limit the information the site collects to the fact that you are under 18, and nothing else. It’s an application of the principle of least privilege. It lets you give the website that one fact without revealing your name, birthdate, address, browsing history, and all your other private data.
The idea is that e.g. the government would give you an app that lives on your phone. When you apply for the app you provide some documents to prove your age, but you don't say anything about what sites you plan to visit. When you want to visit an age-restricted site you use the app to generate a proof that you have it, but the site doesn't learn anything more than that, and the government doesn't learn that you used the app.