Because of the Full Faith and Credit Clause, I expect that also effectively eliminates a lower age for other states, as long as someone is willing to establish residency in Tennessee long enough to get married there before moving. Any marriage established in Tennessee must be honored by the other states.

Some US states do permit marriage at a younger age than normal if you get some additional sign-off from parents or a judge or something, IIRC.

kagis

https://en.wikipedia.org/wiki/Marriage_age_in_the_United_States

It looks like California, New Mexico, Oklahoma, and Mississippi also have no hard minimum, so we already should be at a hard minimum of zero years old, as long as you jump through the other hoops.

California: With parental consent and judicial approval, a person can marry under the age of eighteen but the partners and the minor’s parents have to meet with court officials who must rule out abuse or coercion. There is a 30-day waiting period for minors unless they are seventeen and have graduated high school or one of the partners is pregnant.[47][48]

New Mexico: With parental consent, a person can marry at 16.[71] A 16 or 17 year old teen can marry with the written consent of each living parent of the minor.[72] A person under 16 can marry with judicial approval and parental consent or if pregnant, or by order of a children’s or family division of district court.[49]

Oklahoma: With parental consent, a person can marry at 16. A person under 16 may marry if authorized by the court.[42][43]

Mississippi: With parental consent, males can marry at 17 and females at 15. Boys below 17 and girls below 15 can marry with judicial approval and parental consent.[49][43][66]

I also don’t know whether it’d be constitutional for another state to prohibit sex between someone and their legal spouse. If I had to make a guess, I’d say no, but not sure. Maybe the right to privacy in Lawrence v. Texas applies.

EDIT: At least in Arizona criminal code, to grab the first state using the term I searched for, it looks like being married to someone is a defense against statutory rape charges:

https://en.wikipedia.org/wiki/Age_of_consent_in_the_United_States

The age of consent in Arizona is 18. However, there exist in the legislation defenses to prosecution if the defendant is close-in-age to the minor or a spouse of the minor. Note: these are not close-in-age exceptions but defenses in court. Arizona Revised Statute 13-1405(A)

D. It is a defense to a prosecution pursuant to section 13-1404 or 13-1405 that the person was the spouse (legally married AND cohabiting) of the other person at the time of commission of the act …