Seriously, lots of people married early back then. My own grandmother married at 16 and it was not unusual. She had already finished high school by that age.
That would have been quite a feat, considering that graduating from high school in the early 20th century was a true achievement, demonstrated by the fact that most people did not accomplish it.
As I wrote earlier, my great-grandmother married at 16, but I know she didn't graduate from high school, and it's likely she never even went to high school; her grandson, my father, was the second in the family to accomplish that, back in '41, with his oldest brother being the first.
But there's another point hidden here, that no one has said as far as I can tell. Mormonism has a sordid past, but a 21st century nation of Mormons, at least from a worldly perspective--what happens to them after they die is a separate issue--would probably form the closest thing to a perfect society. How Mormonism got from Joseph Smith to, say, Mitt and Anne Romney, is little short of miraculous. Contrast that with, say, Islam, which began as a Dark Ages cult, and is in the process of returning to its Dark-Aged practices, to the extent that it ever left them throughout the last 1400 years.