It is a matter of common sense. You can't reasonably control internet usage of teenager (and probably shouldn't). While 5yo is an avid user YouTube and google and it is a good idea to filter things they can get to
You cannot try and refute an argument based on something that is not in the spec and is "common sense" since "common sense" is not a defined value for a spec that has global implications.
Spec shouldn't define what's good and what's not for your children. That's something for parent to decide. Spec defines a "tool" which can be used by parent who thinks it makes sense for them
Then you cannot defend things as "It is meant for X year olds, not Y year olds" when someone decries the feature as easily bypassable.
I would say that the answer for the 5 year old scenario is supervision.
sure. but having several layers of "defense" is still a good idea
I would freaking love it if Youtube had the sense to not serve adult adverts during obviously children's programming.