I think kids in America -- and probably the West in general -- grow up a lot more slowly than they could. I don't think this is necessarily a bad thing, but I do think it's a thing.
For the most part, American kids are not given any responsibilities and most of them spend most of their time in a public school system that is designed to educate mass numbers of kids, meaning that it needs to use standardized materials and can't provide individually-tailored teaching. The classes therefore move at the wrong pace for pretty much everyone -- too slow for some, too fast for others -- and the material is going to be uninteresting to most. This is before we even get into discussions of "teaching to the test", inappropriate subject matter, etc.
If you treat a kid like an adult, they will (IME) usually act like one to the extent that they are physically and cognitively capable of it. Also, effort matters far more than talent; when I was teaching, the student who wrecked the curve was by no means the smartest in the class but she was absolutely the hardest working.