If there is a true correlation at the lower end, it probably relates to couples knowing each other through school, church and community as they were growing up. 5 years means the couple were not in the same school cohort and probably didn’t meet until after college and didn’t spend much time together outside dating.
It seems counter-intuitive in this day and age, but the most successful marriages I know met in high school or early in college and got married immediately after graduation.
When you get up into that 10, 20, 30 year gap, the real age effect is that as the age difference grows, along with fewer common life experiences, it becomes exponentially more likely that at least one partner has had multiple previous relationships and doesn’t view marriage as a permanent thing worth working to save.
If there is a 30 year difference, it is almost always going to be a divorced older man with an uncomfortably young wife who sees him as more a meal ticket than a partner. With rare exceptions, it isn’t a marriage, so much as a service contract.
“If there is a true correlation at the lower end, it probably relates to couples knowing each other through school, church and community as they were growing up.”
I met my wife at the sports car races in Santa Barbara in 1957 which we won and we got married in June of 1958, 56 years ago.