Like many, in “my day” you had to wait until the ring was firmly on the finger AND Granny approved of you. LOL
Most of my friends married young and stayed married. Move on a generation, all 3 of my daughters shacked up with boyfriends at 18 and stayed with them, it took the youngest 7 yrs to marry but they are all good. Move on another generation both elder grandsons have girlfriends in residence.
Maybe young women do enjoy more sex at an earlier age, more sex is certainly available to young men, as they get older the divorce rate is depressingly high and many never find a life partner.
My own view is that having many sexual partners makes it harder to settle with one, especially beyond 30yrs.