The silly journey to adulthood

Yesterday was my 21st birthday, and it got me thinking about how the United States of America judges adulthood. As follows:

Person: Hooray! It's my 16th birthday and I can drive now. I'm becoming an adult!
Government: But you need to have your learner's permit for at least six months before you can get your driver's license.

Person: Woohoo! I've turned 18 and now I'm really an adult. I can vote, and smoke, and everything!
Government: But you're still not allowed to drink alcohol, even though every other country allows you to drink. You can be drafted into the army and die in a war, but we think you're still young to have liquor.
Person: Damnit! (looks into moving to Canada)

Person: Finally! I'm 21 and now I'm a full adult!
Government: But you can't...wait... Oh shit, you are an adult now. Have a nice day.