Mail-order brides have been frequently younger than their husbands.Age disparity in same-sex male relationships was even more historically common than age similarity in such relationships.There is also the issue of whether all age-disparate relationships fall under the definition of paraphilia.Individuals who exclusively pursue age-disparate relationships are generally classified by psychologists as parasexual, that is, their behavior is qualitatively different from the norm.Finally, younger partners may see their relationship with an older person as a way of increasing their status within their society.This phenomenon is colloquially called "gold digging" when it involves a strictly mercenary attitude about money.The most common pattern in heterosexual couples is an older man with a younger woman.
Many psychologists study the phenomenon of age disparity, and have observed certain extremes of the above referenced behavior.
(Such relationships were practised in Ancient Greece, pre-Modern Japan, Melanesia, Islamic lands and Renaissance Italy.) Monarchs have traditionally exercised the freedom to choose younger spouses; Henry VIII, for instance, chose women far younger than himself as some of his wives, and a number of female monarchs have chosen younger consorts.
Sultans from the Middle-East maintained entire harems of much younger women.
There are many factors which draw both young and old into such age-disparate relationships.
Women generally begin to lose fertility as they enter their late twenties, and lose it completely after menopause, while men remain almost fully fertile until much later in life.