So going for the old Wikipedia post on the "age of majority". Good choice I love Wikipedia for a quick knowledge refresher. That being said go look up age of criminality, age of consent, and age of license as the traditional and not to mention legal ages of adulthood while you are at it.
Applying the age of majority as a catch all for the definition of adulthood is a lazy and not to mention legally ignorant argument. So it would be really nice if people would step back and realize they loose the audience when the spout off about things they know nothing about.
You can go to prison as young as 10 for murder in the US.
You can declare your independence from your parents and quit school at 16 without a legal battle. You can do it even younger if you have the means to support yourself.
You can drive at 14-16 depending on which State you are in.
You can join the US military at 17.
You can have sex and get married at 16 in most of the country.
The only thing 18 gets you is the right to enter contracts, vote, and buy firearms.
The funny thing that 18 is just to buy, you can own and possess guns (this includes handguns) at a much younger age. In some states that goes all the way down below the age of 10. In more than half a 12 year old can hunt anything, with just about anything and get this....do...it...by...themselves.
Yes that means if little Timmy wants to go hunting for bear with a very large caliber rifle. He can. No problem. As long as he can pass the safety class and is strong enough to carry the rifle he is good to go.
I'd have a second think about what the "age of majority" really means, and blow your highly uniformed opinion out your ass..