Authentication & Authorization is a OS feature. But instead of the OS collecting everyone's age, just give parents the ability to verify their child's phone is in child lockdown mode. Then the phone narc's to the website: "the user is under age". Not "the user was born on Feb 29 2001." We can rely on parenting to ensure a child doesn't have a non child mode phone. Enable parents, not control everyone.
OS vendors don't want to add this feature, though. That could be because they make their money from a percentage of IAPs and ads. And when they are mandated, like in Brazil, we HN commenters hate that even more, because apparently in Brazil it's illegal to sell a phone without locked bootloader, or an OS that can run software from outside of an app store, because the user might install an OS or an app that doesn't co…
Firstly traffic can be tagged by ISPs/cell phone companies, at the bill payer's behest (whose name and age has already been verified). Secondly, smartphone OSes can tag traffic at the behest of parental controls (which already exist).