I see social media age verification is being justified using phony “science” about young people's supposedly-underdeveloped brains being uniquely vulnerable to addiction.

This is a myth. There is no such thing as a fully-developed brain. Adults are every bit as vulnerable. If they weren't, there wouldn't be a monstrously profitable underground market for gambling and narcotics.

And no, tobacco smoking isn't falling out of favor because it's illegal for kids now. That doesn't do squat; there is absolutely nothing stopping parents from giving cigarettes to their kids.

It's falling out of favor because Millennials decided smoking is cringe and stopped doing it.

If social media algorithm addiction is a problem, then that sort of cultural change is what will solve it, not the decree of some ham-fisted politician.