OK, fair enough, but this is pretty clearly a function of patriarchy, not nature. This is from the link you posted:

"In many societies, girls are under pressure to marry and bear children early. In least developed countries, at least 39% of girls marry before they are 18 years of age and 12% before the age of 15. In many places girls choose to become pregnant because they have limited educational and employment prospects. Often, in such societies, motherhood is valued and marriage or union and childbearing may be the best of the limited options available.

In a patriarchal culture, the most valuable and most expected thing a woman can be is a mother. Women and girls will have even fewer opportunities than boys and in some place, may literally have no other options or value as a person. But that's not the only sort of culture that we've ever had as a human beings. In fact, it's a pretty recent one. In many ancient cultures, women were business owners, physicians, judges, priestesses, etc. Take that away and posit women as nothing more than baby factories, and suddenly you've got 13 year olds getting fobbed off to some old man. Overwhelmingly, they aren't marrying other 13 year olds. That's culture, not nature.