That uptick for men at the end of the 1970s is me. It had been the world till then that you married the last girl you dated at university, had children and settled into life. I was not prepared to do that, nor were, apparently, others. as these stats make clear.
The median age at first marriage has risen dramatically in recent decades. Historically, the typical American women married between ages 20 and 22. From 1947 to 1972, the median age at first marriage for women ranged from 20.1 (in 1956) to 20.9 (in 1972). What this median number means is that the first-time bride in 1956 was more likely to be 18 than to be 23. In such an culture, most young men took a serious approach to their romantic pursuits, because by the time a man reached his early 20s, most young women were either already married or engaged. High-school boyfriend/girlfriend relationships often led directly to marriage and there were relatively few single people older than 25. The birth rate was substantially higher then, so that the typical 25-year-old man during that era was working to support a wife and two children. A teenage boy could see all around him the same pattern, and follow the familiar steps of a path — finish high school, get a job, marry his girlfriend, have babies — that would lead him toward the role of responsible adulthood by the time he was 25.
This social script has been torn to tatters in the past 40 or 50 years. In 1973, the median age at first marriage for U.S. women reached 21 for the first time in more than two decades, and has continued rising steadily — to 23 in 1980, to 24 in 1991, to 25 in 1998. The median age at first marriage for men, meanwhile, increased from 22.8 (in 1966) to 27.1 (in 1996). What this means, culturally, is that adolescence has been extended and adulthood has been postponed, so that the typical 25-year-old American man nowadays is more irresponsible and immature than his grandfather was at the same age, and this postponement of maturity has social consequences.
Marriage is middle and upper class. It is for grown-ups, of which there are fewer every year.