Most sources say (early Church fathers and Saints) that there was likely a 15 year difference between Mary and St. Joseph, but we have to admit there relationship was extremely special and different to what most of us will be experiencing in marriage (i.e. she remained a virgin).
Unfortunately, two separate time periods in the last century influenced virgin culture quite a bit. . . World War II was one of them. . . a girl could remain a "nice" girl if, for example, she sent her sweetheart off to fight with a night to remember, with the social mores of that time. Even "Victory Girls," the women who slept with soldiers and sailors during periods of leave, etc. were not considered as morally unacceptable in that time period as they would have been 10 years earlier or later. First-wave feminism started in World War I, when it became necessary first for women to be Yeomen the Navy (clerks/secretaries), tied to some women working in non-traditional jobs (not to the extent of the latter war), and suffrage. This generation of women were to become flappers (girls who partied and flirted but still maintained some degree of purity), and also to display attitudes encouraging women to compete openly in sports, and to wear slacks in casual situations in the 1930s. . . this would go to an extreme during World War II, when women were forced to be breadwinners, support the war effort, and were permitted to enlist in all branches of the military, not just as nurses in the Army and Navy or as secretaries in the Navy. They were needed to help train men, run planes, run plants, run businesses, and run households without male advice. . . first wave feminism was at its peak during the early 1940s.
After the war, virginity returned to the most desired status, and couples began marrying when they were closer in age, as the GI Bill allowed men to have some income and education options at an earlier age, even if they were not upper class men. But the displaced mothers and sisters would later light a spark in their daughters and younger sisters to not just see post-war suburbia as the only option. . . and that the altar wasn't the only option. This increased with the invention of oral contraceptions and social commentaries like "Sex and the Single Girl," which conveyed the belief that women could choose discrete sexual partners without being immoral. . . Bond girls fall into this category. . . and this attitude surfaced in the early 1960s. Secretaries were often "more than a secretary," and often, their goal was marriage. . . but as the 60's progressed, their goal was often to rise to higher level positions and careers, with or without using sexuality to enhance opportunities.
By 1970, when "Mary Tyler Moore," debuted, second-wave feminism was giving way to the third-wave. Women were told they could be happy without marriage as their ultimate goal and that work families could be just as fulfilling as being a wife and mother. Mary's character WAS to have been a divorcee, but there was concern that viewers would confuse 29-year-old Mary Richards with the older character, Laura Petrie, a prior role. Instead, it was revealed during the first season, subtly, that Mary had LIVED with her fiance, and worked a good job while he received more education, then he still had cold feet after three years of co-habitation, leading her to move to an urban area. Mary was seen as positive, but she was not a chaste woman---it was regularly, subtly conveyed, that while she was choosy, she still chose sexual partners, while other characters on her program, and eventually, on other shows (especially those produced by Norman Lear---"The Jeffersons" excepted), were free to pursue co-habitation and pre-marital sex without being morally corrupt. . . society followed these trends into the disco era, and equal pay for equal work, as well as changing sexual values made free love rampant.
The current US culture is marred by these changing mores; only HIV put an end to the free-love era of disco. . . .even in conservative circles, to some extent, and due to the perceived need for two incomes, the need for both males and females to have post-secondary training to have gainful employment as a young, single adult and newlywed, etc. we have the marriage age higher for both men and women than it was in the past. . . and statistics usually prove the higher the age, the less likely the person marrying (male or female) is to have refrained from pre-marital sex. . .