I want to be able to hire a licensed Identity Service Provider that gets all of my verified identity data in an encrypted token and let me register it with the OS, and control what amount of the data I expose to apps, with age verification being one of the lower levels of access.

I pay the company to verify me, I am their customer. They take on the liability of the OS makers and app makers of age verification.

If you have a valid token signed by a licensed IDS that verified your age in your OS, that's all anyone needs to know.