When my grandmother married she was a teen - I think 16 but definitely an even number, in my recollection, and not 18. She married a widower whose son survived the illness which carried off his mother and sister. I dont know how old my grandfather was, but it obviously would have been 25 at the least.I read about Ireland that the reason they were known as the fighting Irish was that men didnt marry until they inherited their fathers farms - and thus, functioned pretty much like adolescent boys into their 20s and beyond. And in those circumstances the men would - very ordinarily - marry women ten or more years younger than themselves.
It would certainly seem to be a recipe for the women to routinely be considered immature, when compared to husbands so much their senior in age . . .
There's a biological reason for this. An older man who wants children would want a wife who was closer to the beginning of her child-bearing years, rather than at the end of her fertile years.