No he's not because the experiment doesn't depend on them. Social science researchers use these kinds of sudden differences in laws all the time to study their effects. People in general can look at the outcomes too if they're obvious enough.
I don't think it's very likely we'll get any actionable data out of this. It doesn't actually stop children from accessing social media, or even creating accounts on social media sites. Tracking social media usage by children will depend entirely on self-reported data and there are an endless amount of confounding variables that would make a direct comparison of children's mental health difficult/impossible to attribute to this one change.
Digital IDs are becoming more and more a thing. Soon it will be quite easy to validate that someone is over 16 or require a parent to provide their ID and vouch instead.
This is an old way of thinking and with some recent developments more of the wild west internet will die.
