The age of breading relationships has changed over the last 100 years or so, as mentioned. Birth mortality rates have plummeted for both mother and child. Before, having a younger wife would have increased the survival chances. Not necessarily only at birth, but through the development of the child (14 years or so). Also, it was also necessary to have more than a 2.5 family because of general mortality rates. The survival of the family tree required larger families.
We now are living in a time of great prosperity, in terms of food, natural disaster and disease control. (Hey, JDubs, bet you don't agree with that!). Our society is no longer focused on survival. I'm not suggesting that was the only focus for relationships, but it was one of the primary foci. All my grandparents come from families of between 12 and 16 siblings. You can't start that kind of family at 29.
The changing morality of society is also a factor. This changes, usually following references from outside factors. (One of the reasons that following any ancient text 'word for word' is just plain stupid). In our western philosophy it is now regarded that having a relationship with an emotionally and physically immature person is wrong. I'm sure if we went back to the 'hard days' that would change.
I personally don't understand why anyone would have a relationship with an adolescent. They bore the f**k out of me after a day. I can't help thinking that there is some father / child relation happening. Or some insecurity on both parties. But that's just me.
WLG: After reading the posts about your old town, I have to ask, where was the banjo playing albino ?
steve