most happy and healthy kids have a unique desire to learn and trying to suppress that is unhealthy
things like screen time, finish your plate, etc
screen time is just a limit on time to learn if the kid is using it for the right purposes which you should teach them to
“finish your plate” I was never told that as a kid and I devour anything that is given to me
Knowledge and wisdom are not the same. Wisdom is knowledge compounded by experience. The examples you list are not wisdom, nor are they necessarily knowledge. They are parenting techniques with obvious flaws.
As for 18 being the magic number, that’s pretty societally arbitrary. Sure, one is legally an adult at 18 in many societies, but that doesn’t mean they have life experience to amount to having wisdom. Many 18 year olds know enough to function in society, but they’re realistically still children from a developmental standpoint. There’s no magic age for anything.