Because it's not that crazy or authoritarian and is basically what most websites already do to "verify" you age (which is to say nothing but asking you your age). But the onus is now being put on OS makers, with an additional clause to build an API for other developers to access so they also can "know" a user's age.
The law does not require photo ID uploads or facial recognition, with users instead simply self-reporting their age
Maybe. But it will be funny for a little bit when the data starts showing the average age of a Californian is over 200 years.