Ultimately, it is the age at which the woman begins bearing children that is the biggest factor in survival, the paper in suggests: Younger women, in general, bear more healthy children.
Marrying an older woman or much older man proved the most detrimental to reproductive success.
The rule would theoretically create a paradox for people under 14, because the younger partner would have to be older than the older partner, but 14 is about the youngest you can be and make anything even remotely resembling adultish decisions respecting relationships anyway, so this rule works out rather well.
This has the advantage of allowing for a larger age gap the older the partners get; the four-year age gap between a 22-year-old and an 18-year-old is significant (and just barely allowed by this rule), but the same age gap between an 86-year-old and a 90-year-old isn't worth comment.
Age-disparity relationships have been documented for most of recorded history and have been regarded with a wide range of attitudes dependant on sociocultural norms and legal systems. Relationships with age disparity of all kinds have been observed with both men and women as the older or younger partner.
Another study also showed a higher divorce rate as the age difference rose for when either the woman was older or the man was older.In its earliest appearances, this rule is often cited as having French origins, although this citation always seems to appear in English-language (British or American) sources, leaving its true origin mysterious.Another, somewhat vaguer metric often cited is declaring an age gap creepy when a partner is "old enough to be your mother/father," carrying with it as it does implications of symbolic Parental Incest or Wife Husbandry.The span ranged from men marrying women as much as 20 years older to women marrying men as much as 25 years older; the average age difference between husband and wife was three years.Marriage customs or the availability of reindeer to support a new family (the Sami people are reindeer herders) might be the reason that more Sami marriages did not display the optimum age difference, Helle says.In August 2010, Michael Dunn of the University of Wales Institute, Cardiff completed and released the results of a study on age disparity in dating.