In many states, there isn’t even a lower limit, as long as the parents approve of the marriage.

http://en.wikipedia.org/wiki/Marriageable_age#North_America

That’s not to say that they’re allowed to have sex, though. This also differs from state to state. The lowest age of consent in the US is 16, and it often requires the consent of the parents.

http://en.wikipedia.org/wiki/Age_of_consent_in_the_USA#Unite...