This is the best solution I've seen, and it's also the simplest. No authority is involved other than the parent. No complicated protocols, or heavy CS theory about privacy preserving algorithms. Just one setting, "this device belongs to a minor" and apps either honor it or they are not allowed in the App store. Will some parents turn it off for their 14 year old? Yes, but some parents buy beer for their 14 year olds. That's a different problem.

Apple, Google, and the social media companies could have done this 10 years ago and we would not even be having this debate today. But they decided they didn't have any social responsibility for what their devices and software did, so here we are.