The biggest damned issue i have with the "child / teen / adult" markers is they would literally serve up minors to predators.
Malicious sites already use browser markers to tailor exploits, now they can scoop up the kiddies with ease. A 14 year old browsing substack is currently just another random user. But put in OS level markers and now they're spotlighted.
That's the irony. It would make kids more fucking readily ltargetted.