How old do you have to be to get married to a U.S. citizen if you are a citizen of another country?

You need to be at least 18 yrs of age to get married to a US citizen. Some countries have a higher or lower age limit slab. 18 yrs is the time when an individual is said to be mentally mature to take on the responsibilities of life.

The same age if you were a citizen. It varies from state to state but it's generally 18 or 16 with parental consent.