The Time of His Life by Larry Eisenberg

The Time of His Life by Larry Eisenberg (F&SF, April 1968) opens with the scientist-narrator brooding about his life—not only has his early promise failed to amount to anything, but he is beginning to tire of married life and fatherhood. Added irritation is provided by his Noble Prize-winning father, who not only didn’t acknowledge the son’s contribution to his prize-winning work, but now chides him for not pulling his weight and for having an affair with one of the graduate students who works in the lab.
Later on in the story the father summons the narrator-son to his office, and there follows a conversation about the direction time flows. The father then reveals an artificially aged monkey, and tells the narrator he wants him to slow down the field fluctuations that cause the effect.
While the narrator works on process, there are further arguments between the men about the narrator’s extra-marital relationship. Then the son sees that the monkey is young again and, when he reveals this to his father, and suggests himself as a human test subject (hoping to become the same age as the grad student and restart his life), the father shows that he has already tested the method on himself when he removes a wig and makeup to reveal his younger self. When the narrator says he also wants to be twenty years younger, and that his father can have his wife and children (we are told earlier he is an attentive grandfather), the father mocks the suggestion, if only because of the questions that would be raised when his older self vanished.
The narrator subsequently goes on a multi-day drunk and (spoiler), when he wakes up, discovers he is now as old as his father—he realises they have swapped places but, in a final twist, shows he doesn’t care—he is the one who is now the Nobel Prize winner.
This has a cleverly convoluted plot, but one that doesn’t stand up to much scrutiny (e.g. the makeup scene). However, the warped, almost reverse-Oedipal father-and-son relationship is intense and weirdly fascinating, as is the son’s acceptance of what happens at the end of the story (it would have been easy to have this as a straightforward victim ending).
*** (Good). 3,500 words. Story link.