We have decided as a society to age-gate the purchase of a very small selection of goods and services, but this did not require a law that says all merchants have the right to know your age. And in this case, it's not even just all merchants, but anyone that serves you any kind of information. The real world equivalent of this California bill would be more like: anyone you've ever talked to has the right to know your age.

A more reasonable approach would be for parents to keep tabs on (or for stricter parents, control) who their child is associating with and where they're going, and advise their child on who/what to stay away from if they're out alone. And of course that takes parenting effort. The digital equivalent of this are things like password-gating app installation in the OS and website-blocking in the WiFi router. But I will say, I don't think these kinds of analogies are good because the Internet is too different from the physical world.

And let's not underestimate the tracking power of a legally mandated data point: the age contains about 6 bits of information that can be used to identify your user account on the Internet across apps and websites, even if your inputted age is fake.