Today a wife has to be at least bat mitzvah age. And under secular law in the US, a wife has to be older in almost all states, even with parental consent.
Excluding the evil divorcees who figure they can get back at their spouses who gain full custody of their female children.
I remember a case way back, and it was a real problem.
BTW, there is no reason in Halacha why a girl can not get married off at birth.