One of the most nuanced, unexpected Cheers episodes. Sam starts diving headlong into a midlife crisis, dating young women and overexerting himself at sports.
When Sam suffers a hernia playing Woody at racquetball, he hides his going to the hospital - Diane tracks him down and insists it's okay to accept growing old. Sam bristles at this and checks himself out of the hospital.
However, Sam suffers a relapse and returns to the hospital, where Diane announces that he was right - he shouldn't accept growing old, pointing out many great figures who performed great deeds well into old age. Sam is aroused by Diane's speech - she gives the classic line as Sam advances on her: "Oh, Sam, this is wonderful. An old person wouldn't be doing this. This is the act of a vital, strong, young man. Who wants a woman. Who wants sex. (Sam gets too close) Who won't GET it..." After Diane departs, Sam meets his new roommate, who is basically a blond version of Sam. They bond, discovering that they're both getting older but have plenty of virility and drive. However, when the man introduces a young woman to Sam, Sam hits on her - then discovers she's the man's daughter.
After the man leaves the room, Sam becomes introspective - he sits quietly at the hospital window as it rains.
While the episode remains lighthearted through most of the episode, it refuses to give an easy answer. The message of "You're as old as you feel" is subverted as Sam realizes that while he's not an old man, time *is* slipping away. His counterpart had a daughter, and was presumably married, while Sam is a bachelor and childless. How much time does Sam have left? This episode was typical of the gravitas the Sam character had during the "Diane years" - an alcoholic womanizer who was struggling with life. Sam would never recover it til the last few episodes of the series.