Age verification can be done by a third party, so that the online service isn't provided with any details of your identity, just that you passed an age verification check.
But if you're still worried about online pornographers getting a copy of your identity, maybe don't use their websites? It's an easily avoidable risk. Perhaps use your imagination instead, or read an erotic novel bought in cash from a second-hand bookshop, or something like that.
That third party? Persona.
Do you hear yourself? You're a guy telling people that if they don't want to be put on a list for reading a book, they should read other books.
> erotic novel bought in cash from a second-hand bookshop
Your confidence that this will remain an option probably means that you aren't aware of the many court battles, lives ruined, and leftover frozen conflicts resulting from attempts to publish novels. Its a confidence you could only have developed since the mid-1960s.
There is absolutely no physical reason why the government couldn't record all of the books you buy, arrest secondhand booksellers that don't keep those lists faithfully, and even sit outside of secondhand booksellers identifying everyone walking into the building and putting them on a list of people who are interested in obtaining books through unorthodox methods.
If everyone had been like you, there wouldn't be erotic novels available from bookstores. Or communist novels, or gay novels, etc.. And through the mails, it would become federal. The government mainly opened mail to search for possible birth control information being sent.