Meh. I was a kid once. I was smoking weed at 15. Gave it up at 21 or 22. I think it should be completely legal. FOR ADULTS. A person needs to reach the age of majority to legally make decisions for themselves. Dangers of drugs and alcohol need to be taught by the parents.
In my opinion and experience, I think the real danger in weed is seeing how harmless it really is compared to other drugs(tobacco, alcohol, prescription, and street drugs). I wouldn't say that it's a gateway drug. Especially for people who have self control. But it's very easy to assume that other drugs aren't as addicting as weed, and before you know it, you're a full blown alcoholic or balls deep in an opiate addiction.
I was born with the part of my brain that says "man, that feels really good. Let's do it again!!" So I don't do drugs and I hardly drink anymore. Meanwhile, I lost one brother to fentanyl and I've watched my other brother nearly kill himself a few times detoxing from alcohol. They had to put him in a coma for the withdrawal. It wasn't pretty. And I've had too many close friends growing up go into harder drugs and they're no longer around.