There are obviously certain harms we are comfortable (trying to) prevent 13yos from having access to. So it's a matter of degree.

The internet you describe has been gone for a long time. The internet that replaced it is several degrees more harmful, to adults and children alike.

So maybe instead of trying to control the people we could try controlling the corporations responsible for this problem? Bring back the old internet. Make addictive services and algorithmic recommendations illegal. Make commercial entities more responsible for the services they offer.