You're right in that, setting aside future laws which might build off of the California Digital Age Assurance Act, the text of the law is compatible with privacy because adults or children can lie about the age info, perhaps with no legal consequences for doing so.
I was wrong to say:
> Adults cannot choose to withold both their own age info and the age info of their children. Older children in abusive parental situations cannot both get their own (standard) devices and withold their age info.
I fix both sentences by adding to the end of each one "unless they lie about the age info".
The other parts of my previous comment remain unchanged so far:
> The California Digital Age Assurance Act forces operating systems to collect age info.
[...]
> I oppose such an implementation because a more privacy-respecting implementation is available: the government could mandate that operating systems provide device owners with an option to reveal their age info or their children's age info.
Are the proponents of the California Digital Age Assurance Act satisfied with the law despite the elephant-shaped "they can select any age they want to" loophole? If not, then the spirit of the law does not respect privacy. If yes, I would still oppose the law. I want both the text and spirit of the law to respect privacy, not merely be compatible with privacy. An illustrative example: even if there were a technology or magic that literally prevented law enforcement from searching a house without a warrant, I would still want the legal system to have a law (in the constitution, specifically) recognizing a right to have one's house not be searched by the government without a warrant.