Algorithmic? I think simply checking like the US law "ID 18 U.S.C. 2257" already does is a much better solution than having algorithms guess the age based on a photo or video.
Though I have to say I sometimes wonder how sites like Onlyfans do this with male actors. Often the only thing you see is their dick and I can't remember having to submit a dickpic for my passport :D So how do they know a submitted passport matches the dick in question?
But really I think it's better to know for sure than to guess.
Laws just don't matter. People physically can't look adults/kids if they're from "wrong" cultures whether they were 60 or 16 and put GP into hot water by appearance.
Sites like Onlyfans, or any website for that matter, just delete contents based on appearances and user metrics. Otherwise escalations won't stop; users would leave, protest will occur, new laws will be created, state committees will be formed and blacklists are made, and credit card processing suspiciously starts failing. Recordkeeping is for honest people to be honest if they want to be. Some numbers on a driver's license do not stop the horde from banging the walls.
So a truly global feed has to hide inconvenient contents from users until users are ready for it. Ideally user editable. Which is what everyone is fat-finger doing at server side anyway.
Though I have to say I sometimes wonder how sites like Onlyfans do this with male actors. Often the only thing you see is their dick and I can't remember having to submit a dickpic for my passport :D So how do they know a submitted passport matches the dick in question?
But really I think it's better to know for sure than to guess.