Earlier quoted context omitted.
Zero-knowledge methods for verifying age are possible but there is almost no political will or interest in them. Sites would get a “yes” or “no” as to whether someone is of age, and no other information.
They could verify ID, associate you with an "ID verified" token, and immediately trash all the information they collected other than that token.
Similar thing happened to Valve; people were trading gun skins, and regulators fined them for not having AML/KYC controls because the state argued "the business didn't do enough to stop money laundering."
This trickles out to porn companies (and the vendors that use them for identity verification), and implies that they need to store this data to prove that they didn't delete it to help terrorists.