"These men averaged thirty-six years of age (range: 24-60) and had been married an average of ten years (1-32 years) before marrying a second wife of a mean twenty-five years of age (14-39 years). At that time, their legal wives averaged thirty-two years of age (22-56)."
I haven't found a good dataset, but this book has this comment: "Latter-day Saints were surprisingly obedient to the counsel to marry, and in 1860 Manti, only 1.6 percent of women over the age of 16 had never been to the altar." I believe 14 was the minimum legal age of marriage for at least part of that time, so that would mean almost all women were married between 14-16. Depending how many of them re-married after being widowed or divorced, or how many older women migrated in for marriage, I'm not sure what the overall stats of 'age at marriage' would look.
I've always wondered at the historical accuracy of "A Study In Scarlet", but its depiction of the social climate regarding marriage among the LDS would appear to be spot-on...
If only 2% of women over age 16 as also under age 18, that statistic is not so shocking. I don't agree that this statistic alone demonstrates that "almost all women were married between 14-16."
"A study in scarlet" is not historically accurate. IIRC, Conan Doyle said so himself.
Even today, the median age for a woman having her first child in some poorer countries such as Niger, Bangladesh etc. is 18 years[1]. That means a lot of them are younger than that. If you get a group of ten 15 year old girls from Bangladesh, statistically one of them will be nursing their first child.
So let's be careful to judge history by the standards of today. Sure, some of this was mormon practices, but other parts of it was just because these people were doing the same thing most poor peasants on the rest of the planet were doing and considered normal.
1. https://www.nationmaster.com/country-info/stats/People/Mothe...
2. http://www.hips.hacettepe.edu.tr/nbd_cilt35/nahar_zahangir.p...