As little as a century ago, marriages as young as 10 were not unheard of.
In any case, in Western culture up until a couple of generations ago, it was the norm for a man to go out and establish himself in his trade and have a viable career, and then go find himself a wife of prime childbearing age. Age gaps of a decade or even two were normal.
Over the last couple of generations the gender roles have blurred (Ashton Kutcher and Demi Moore, anyone?) but the biology hasn't. There is a reason men are capable of reproduction to much greater ages than are women. Whether you view that as the way we were made, or an adaptation ala Darwinism is irrelevant to the facts.
Western culture had such age gaps as common, even the norm, when life spans were shorter and childhood deaths were common. You started young and produced as many children as you needed to. Elements of this, such as age gaps, were still the norm 40 years ago, even 20 or 10 years ago, even though the root motivations such as child deaths and shorter life expectancy had diminished. To criticize such practices is a contrived excuse.
Very wonderful and informative post. Thanks, calenel.