21 is the drinking age.
You have to be 19 to buy cigarettes, except on the reservation.
You can drive at 16.
There really isn't an age it's legal for you to have sex. There is an age of consent, which is the age in which you're legally allowed to have sex with someone over the age of 18 but it's different in each state, here it's 17.
You can't legally move out until you're 18 unless your parents give you permission.
I'm in New York so my laws differ a little...
Moving Out--16
Driving--16
Tobacco--18
Sex--18
Gambling/lotto--18
Drinking--21
(I know you have to be 19 to buy tobacco in New Jersey.)
You can join the military at 16 with parental consent or 18 without.
Marriage... You can get married at 14 with a judge's OK, 16 with parental consent and 18 without.
Some people (myself included) believe that if you are old enough to go to war then you are old enough to drink and want the drinking age dropped back down to 18 (it used to be like that about 20-something years ago).
It doesn't matter if you are American or not, they'll still card you for everything. I have to say though, I really enjoyed actually buying my own beer when I was 19 and I visited Ireland.