I've seen the studies that talk about census figures, but they are from 1890 and beyond. I don't dispute them.
In the 1800s the legal age was as low as twelve years old for females
An interesting but limited study of a geneological site, showing "average" and earliest ages for the last 5 centuries.
I doubt that the "average" marriage age was ever much into the teen years, because of statistics. Suppose the average age was 18. For that to be true, for each woman of age 40 who gets married, you need to have 11 16-year-olds get married.
The median age would be more informative than mean, but I doubt the median age was all that young either.
But I also have no problem believing the age of marriage was much lower than it is today.
Be wishy-woshy about mean, average (same thing), or median...It doesn't matter. It was not typical, or regular, or normative, or standard, or commonplace throughout 19th century society for young teenage girls to marry...
And, yet...it was quite commonplace, normative, standard, regular among the LDS society. JUST LIKE THE FLDS, TODAY.