In older cultures (Europe, ME, India) and much of the US in the 19 and early 20 centuries men did not marry until they were established with an income and demonstrated ability to support a family. They then sought older teen age girls to marry. A girl 17 in England could expect to marry a man in is mid 30s to early 40s.
My great, great grandfather lost his wife wen e was 55. He had 6 small children and married a girl 16, the age of his oldest child. The new couple went on to have 7 more children. One was my great grandfather.
Young men in their teens and twenties rarely married until the industrial revolution allowed younger men to have a steady, dependable income. Marriage used to be about the ability to support a family.
I read somewhere that that effect was especially pronounced in Ireland, where a man didn’t marry until he inherited his father’s land. Thus, Irishmen in their twenties behaved a lot like teen-aged boys - and hence the nickname, “the fighting Irish."