What problem are you trying to solve?

Users may not want to have content that is meant to be restricted to adults displayed in their browser. Thousands of sites already label their content as such with a meta tag because they do not want to distribute their content to children. Some OSs provide account-level controls for enabling web content filtering for a user. However, these are not plumbed together in the browser.

What solutions exist today?

Users can install browser extensions to do this.

Currently, governments seem to be turning toward cryptographic proofs of age from digital credentials to make similar use cases work. Even with fancy crypto, there are significant privacy risks.

How would you solve it?

Add insertion steps for the meta tag with name="rating" to halt the document's parser, disable scripts, and redirect the user to an error page.

Anything else?

This is in support of finding a better way to do age verification online. There's a workshop happening about it next week with a lot of position papers: https://datatracker.ietf.org/group/agews/materials/.

Several of the positions point to self-labeling like this as a least-bad option, including my own.