I'm trying to understand how this is even a bad thing. Where is the privacy invading verification? Surely a given OS can implement the API response however it wants? If you're root, tell me your age. If you're not, (a child account), the admin (their parent) sets the age. Seems fine?
Well, it's not a bad thing. And if you can root your own computer, that's adult enough
Y'all are like Dilbert with the shock collar on, "It's not so bad." It's requiring all operating systems, apps, and online services to add age checks. It adds friction to the process of developing stuff. If there's something you do not want to do especially in California of all Goddamn places (swear to God, Wozniak would be spinning in his grave if he had one) it's add friction to the software development process with government-mandated code paths. But what do I know. This is a site actually called Hackernews, where the answer to all large-scale social problems is "that's why we need more government regulation".
Even ignoring everything else, at a minimum it is backwards.
There is no reason to tell the application, and by extension their developers, how old the user is. The application should tell the user what bracket it is appropriate for and then the operating system could filter appropriately without any of the user’s identifying information leaving their system.
This is also technically superior because it moves the logic for filtering out of being custom implemented by each and every single application to a central common user-controlled location; you do not have to rely on every application developer doing it right simultaneously.