Greybeard by Brian W Aldiss

Human reproduction has ceased and society slowly spirals in this "adult Lord of the Flies" by a Grand Master of Science Fiction (San Francisco Chronicle).
After the "Accident," all males on Earth become sterile. Society ages and falls apart bit by bit. First, toy companies go under. Then record companies. Then cities cease to function. Now Earth's population lives in spread‑out, isolated villages, with its youngest members in their fifties. When the people of Sparcot begin to make claims of gnomes and man‑eating rodents lurking around their village, Greybeard and his wife set out for the coast with the hope of finding something better.