A May-December romance is one that occurs between two people significantly far apart in age. How wide that gap is can vary, depending on one's point of view.
This sexy movie centers around a May-December romance between Stella, an overachieving 40-something divorcée and a handsome 20-something whom she meets while vacationing in Jamaica.
— Karla Pope, , 2 Feb. 2021
Why those two months? Think of the calendar as a metaphorical timeline of a life. January is when things begin anew (represented by a New Year's baby). May is spring, representing youth, when everything is newly flowering and fresh. December, at the end of the year, symbolizes the winter of older age, though as our example shows, the older person in the couple might still have a lot of years ahead of them.