YOU may be surprised to learn that when researchers asked people over 65 to pick the age they would most like to return to, the majority bypassed the wild and wrinkle-less pastures of their teens, 20s and 30s, and chose their 40s.

We are more accustomed to seeing the entry into middle age treated as a punch line or a cause for condolences. Despite admonishments that “50 is the new 30,” middle age continues to be used as a metaphor for decline or stasis. Having just completed a book about the history and culture of middle age, I found that the first question people asked me was, “When does it begin?” anxiously hoping to hear a number they hadn’t yet reached.

Elderly people who find middle age to be the most desirable period of life, however, are voicing what was a common sentiment in the 19th century, when the idea of a separate stage of development called “middle age” began to emerge. Although middle age may seem like a universal truth, it is actually as much of a manufactured creation as polyester or the rules of chess. And like all the other so-called stages into which we have divvied up the uninterrupted flow of life, middle age, too, is a cultural fiction, a story we tell about ourselves.

The story our great-great-great-grandparents told was that midlife was the prime of life. “Our powers are at the highest point of development,” The New York Times declared in 1881, “and our power of disciplining these powers should be at their best.”