This wouldn't be a problem if the U.S. had decent privacy laws that were enforceable against both private companies and the government, as well as some form of

This wouldn't be a problem if the U.S. had decent privacy laws that were enforceable against both private companies and the government, as well as some form of actual government issued ID. The German constitution actually provides for a "right to informational self-determination", i.e. any individual has the right to decide what happens with their personal information, including what websites they visit. We also have a standard governmen-issued ID. In combination that makes it possible for private companies to offer web-based age verification, that check you ID-number against a government-provided service, verifying the age but not providing additional information. And because of the privacy laws, it would be a criminal offense to store the identity of the person being verified or for that information to be connected with the website you visit. The website in turn gets a legal record that they verified the age of the person, but not necessarily the actual identity of the person. Ideally, in the end each party only gets a piece of the total picture but by confirming to each other that the piece they have checks out, you can confirm your age to a porn site without any single party being able to piece the entire picture together.