Meta == Phillip Morris - This is a public health issue and will likely need to be treated like tobacco. Kids can't vote so I don't see the political motivation.
The solution, however, isn't prohibition or age restrictions; it's either regulating the algorithms or holding these companies responsible for the adverse outcomes their platforms contribute to. Safe harbor laws made sense when tech wasn't filtering/promoting content, now that they are influencing the material we see, these laws must no longer apply.
This may mean adopting a modern equivalent to libel laws. Something akin to: if an algorithm pushes false information, the company behind the algorithm can be sued for harm. Disallow terms of service that force arbitration or cap liability limits.
When I was 18 the legal drinking age had just been reduced to 18. That only lasted a couple of years. I don't think I'd vote for lowering it to that age again actually.
So what you are describing is just the base case.
It really isn't a bad thing for kids to be told they can't do something occasionally. It kind of helps prepare them for being an adult where it happens all the time.