All of Dr. Hiedegger's friends long for their youth, particularly the physical aspects of their youth. In addition, all four had encountered particulary difficult situations in their lives that they were eager to reverse.
They were all melancholy old creatures, who had been unfortunate in life, and whose greatest misfortune it was that they were not long ago in their graves.
Basically, all of the four friends desperately wanted to return to a time before they experienced their loss. The Widow Wycherly is constantly remarking about her wrinkled hands and aged face. She even wishes she were dead when the drink wears off rather than have lost the beauty she had temporarily regained. Mr. Medbourne had been once wealthy but he had lost his money and ended up in poverty. Colonol Killigrew had spent his youth pursuing "sinful pleasure" which ultimately damaged his body and health. Finally, Mr. Gascoigne had once been a politician seeking fame, but his deceit and lies made him hated for once, and then, later, all but forgotten. Finally, the widow had once dated each of the three men, creating a scandal in the community.
The four are urged to change their ways when they revisit their youth, but Dr. Hiedegger knows they will not. They want, instead, to simply relive what they consider to be the highlights of their lives, not change them for the better.