The modern human species is about 200,000 years old — albeit civilization is only about 6000 years old. I can assumre you that as soon as young girls strated menstruating, they were ready to be married/partnered. In Africa, it is quite normal for y oung girls to become sexually active at 13, and to start bearing children at a very young age.

America is a few hundred years old, and hardly an excellent example of the age in which men and women previously married. In 17th century, England, the youngest a girl could get married was 12, and the youngest a boy could get married was 14. And it had nothing to do with the nobility.