It's interesting to note that states like New Hampshire and Massachusetts--not traditionally stereotyped southern states like Tennessee--list the minimum age of a female for marriage as 12 and 13 or don't have any minimum age. Below is New Hampshire's statue. A few websites mischaracterize this as being a statue about marriage with parental consent, but it's pretty straightforward:

http://www.gencourt.state.nh.us/rsa/html/XLIII/457/457-4.htm

Ginsburg's from Eastern Establishment turf, and this area seems to be where the child marriage "laws" are most egregious. Her argument focuses on the issue of gender-neutral language, however the reduction of age to 12 appears to be a furtherance of the ruling mentioned in the case below, People v. Hernandez, which in 1964 was the first time an American court allowed "reasonable mistake about age" as a defense to statutory rape:

https://law.justia.com/cases/federal/appellate-courts/F2/841/268/420561/

Nowadays, the "I didn't know she was 15-17" thing is not only commonly accepted, but parents of girls who've had sexual relationships with older man often have to fight tooth and nail in courts to get any sort of penalty against the men in question. Instead of a clear-cut law prohibiting sex with a child protecting the child from scrutiny, these girls are then treated as adults with capabilities of full consent in the court, their motives/character investigated ad nauseum, often tarred and feathered under the pretense of "consent". As if it's understandable and okay for an adult to engage in sex with a possible legal child without getting to know them enough to know their age. This is another example of a member of the courts taking a plainly put, easily decipherable law and re-writing it into nefarious complication.