The creeping infantilization of American adults continues.
That assumes that 18 to 20 year olds should be considered full adults. Personally, I don't think they should be, tho to be honest, I didn't think so when I was that age.
They either are full adults who can vote, be drafted into the army, enter into contracts and be tried as adults or they are children. There should be no such thing as a partial adult who can vote and be drafted but can't drink or smoke. The age of majority should be uniform.
That first sentence is ridiculous. Becoming an adult is inherently a very gradual process and one could reasonably argue that the rights and privileges of adulthood should be granted in stages. I don't hold that view, but only because it would be too impractical to implement, and the decision on which things to allow at the youngest ages would likely be arbitrary, but talking about adulthood as an all-or-nothing state is absolutely absurd.