This is an interesting thread from a JW point of view. Early marriage between young people is very common in the Org. Other threads on JWN have recently discussed the reasons.
Age difference between a husband and a wife varies between cultures. At one time it was very 'normal' to marry a young girl - sometimes crossing state lines to make it legal. Young women often - just a few decades ago - married at age 13 or 14. And sometimes to a first or "second" cousin. This kind of marriage was considered acceptable. Often it was a "shotgun" wedding.During that same time period, it was illegal for a man of color to marry a white woman. In the 21st century both of these situations are deemed culturally offensive - in my part of the world. Though still very common in some cultures, an "arranged marriage" seems offensive to the Western mind. A father "trading" his daughters as wives to his male peers is as equally offensive.
A common saying is "follow the rule of seven" - if a man divides his age in half and adds seven years, that's the youngest age a girl can be considered for marriage. Otherwise it's kinda creepy. But, that rule applies in my neck of the world...