Content should be able to send a request asking the OS if you’re old enough to view
You've got it backwards. This is letting them frame the narrative. There's no need to tell anyone else anything about yourself when requesting content. The local device should be where any content filtering happens.
If you're in a kid mode, it should block the incoming content, not rely on a third party to give a shit about blocking itself.
No chance for "whoops we fascismed" that way