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.