You added "Shepherd was about 32 while Mrs. Brown was 49 then."
OK, I'm pretty sure he's making a joke here by modifying the idiomatic phrase "May-December romance." The idiom analogizes the youthful woman with May and the old man with December.
Here, he continues to use "May" for the woman's age, even though 49 is not the springtime of life, and "January" for his own relatively youthful age.
This is a case of an idiom that is so familiar that native speakers can recognize it even if it's changed. Modifying an idiom to express a different situation can be a form of wit. For example, if I decided I needed to give a more detailed explanation of something I might say "Well... to make a long story even longer," changing the idiom "to make a long story short."
By the way there's another sardonic detail you might not have noticed--the phrase "do the wedding bells TOLL..." Bells are "tolled"--rung in a slow, mournful way--at FUNERALS. When church bells are rung at a wedding, they would be rung rapidly and joyfully, and you would say simply "the bells RING." Actually, I see that Google finds a lot of instances of the phrase "for whom the wedding bell tolls" but they would all be jokes--references to an unwanted or unhappy wedding, and--again--modifying the well-known phrase "for whom the bell tolls."
(To make a long story longer... !... "for whom the bell tolls" is a famous line from a famous passage by poet John Donne, beginning "No man is an island" and ending "therefore, never send to know for whom the bells tolls; it tolls for thee," meaning humankind is so connected and the death of anyone is like our own death. Ernest Hemingway used it as the title of a novel, and it has become almost a catchphrase).