Yesterday on Facebook I referred to my daughters, who are in their early forties, as middle-aged. One of their friends, who is 43, wrote, "Middle-aged???"
"For sure," I wrote back. "I know it hurts." But then I Googled middle age and discovered that its borders seem to be shifting. Once defined as ages 40 to 60, it is now often defined as ages 45 to 64  (though Merriam-Webster  wants to have it both ways).
When I turned 40, everyone was talking about the midlife crisis , that scary feeling when people in the workforce fear their careers may have peaked and when caregivers at home notice their nests are practically empty (except for all that stuff in the basement). Midlife hit at age 40 back then — a bit optimistic, perhaps, considering that U.S. life expectancy in 1988 was 74.9 years . Columnist Bob Greene may have been closer to the truth when he wrote that "middle age starts at 36." 
American life expectancy has increased in the last 25 years: it's now 78.62 years . I suppose that makes the shift in middle-age limits understandable, especially since so many people nowadays seem to think adulthood doesn't begin until age 30. But still, isn't Bridget Jones  a bit old to be having a midlife crisis at age 51? And what's with those Brits who, in a 2012 survey , thought middle age begins at age 55 or later? Brits do live longer than Americans, but only by a couple of years.
Despite the fact that researchers have been studying middle age intensively for decades, the term itself seems to have no fixed definition. Nearly any span between 40 and dementia appears to qualify, depending in part on whether we’re talking about ourselves (“But I feel just the same as I did when I was 20”) or all those people who show up at our college reunions (“Everyone looks so old”).
This is probably why some people prefer a descriptive rather than a chronological view of middle age: see, for instance, Shelley Emling's article "40 Signs You Are Middle Aged."  The list is amusing, but the really telling comment comes in her introduction, where she quotes Paul Keenan, head of communications for a healthcare provider. "People no longer see ‘middle age’ as a numerical milestone," he said. "I’m 54 myself, with the mind-set of a thirty-something — perhaps sometimes even that of a teenager!” If anything is a sure and certain indication of middle-age — or even old age — it's a remark like that.
Maybe it's because, at 65, I've just left the ranks of the middle-aged, but I don't see why people want to delay its onset. By the time you're middle-aged, you've probably finished your education and those painful first jobs. Chances are you're in a responsible position, earning more money than you were a decade or two ago. You're probably married. You very likely own a house.  If you have children, they are becoming more independent. Your parents are probably still in reasonably good health.
At 40, you are well past the torments of adolescence and young adulthood, and you still have a long way to go before the serious trials of old age begin. You are at the midpoint of your allotted years and at the beginning of an excellent couple of decades. Why pretend to be young long past the time when anybody who is truly young would claim you?
Believe it or not, those truly young adults respect you. They think you may have learned something in the 15 or 20 years since you left college. At the same time, you're not in an entirely alien world like, say, their parents.
In 1935 Will Rogers starred in a movie called Life Begins at Forty . I suspect it still does.
LaVonne Neff is an amateur theologian and cook; lover of language and travel; wife, mother, grandmother, godmother, dogmother; perpetual student, constant reader, and Christian contrarian. She blogs at Lively Dust  and at The Neff Review .