Pity the baby boomers. This huge cohort — born between 1946 and 1964 — has left its stamp on nearly every American institution. But now that its oldest are turning 65, they do not seem to be coming in for the soft landing they once imagined, characterized by early, leisurely and long retirement. First, the recent financial crisis wreaked havoc on expected financial security. Now the other shoe has dropped.

For the generation that thought lifestyle changes and modern medicine might allow them to live forever, along comes Susan Jacoby to tell them that no matter how many calories they count, how many times a week they visit the gym, and how much faith they put in future miracles of modern medicine, it’s not enough: They will grow ill — from heart disease, stroke and other conditions that afflicted their parents — and they will die.

“One’s real age is one’s real age,” says Jacoby. No matter how young one looks or what cosmetic changes may have been made, a “biological imperative” hits around age 80. The bodies of old people become inefficient, lacking the capacity of the young to repair quickly and ward off disease. Jacoby, the author of eight books and a frequent contributor to magazines such as AARP, offers this sobering news in a new book that will change the way you think about growing old. At least it has changed the way this reviewer thinks.

Browse through a bookstore or library and you’ll come across scores of titles like Successful Aging, Aging Well or, as Mary Catherine Bateson called her new entry into the field, Composing a Further Life. Such books focus mostly on what Jacoby calls the “young old” — those 65 to 75. This is the group marketers target when they tout the possibility of endless youth. Never Say Die takes on a much darker subject. Jacoby examines  the “old old,” those over 80, who are generally ignored by the media and by society because many of them are invisible: sick, poor (having outlasted their retirement savings), often hidden away in nursing homes and hospitals.

Today’s focus on the young old, and on the cheerful picture of aging that pervades our society, has hidden the plight of the old old, Jacoby contends. She set about to uncover the facts, and they are not encouraging. Take the incidence of Alzheimer’s. We are constantly meant to be reassured, she notes, by statements indicating that only 10 percent of people over 65 have Alzheimer’s, and that Alzheimer’s is a disease, separate from the process of aging. Yet the incidence of Alzheimer’s, she points out, doubles every half decade among those over age 80, and half of all people over age 85 will be affected. The likelihood of living in a nursing home also reaches 50 percent once someone reaches the age of 85.

Jacoby is quick to acknowledge that the picture is hardly uniformly gloomy for the oldest of the old. But just because the literary critic Harold Bloom remains prodigiously productive as he approaches his 80th year and your elderly next door neighbor still has all his marbles, doesn’t mean that you or I can count on it too.

Unlike many authors of books on aging, Jacoby doesn’t limit her focus mostly to white, middle- and upper-middle-class professionals. She addresses issues of race, class and gender, devoting an entire chapter, for example, to the sorry plight of women, who make up the largest portion of the old old. In looking at financial issues, she notes that all but the truly wealthy will be greatly affected by changes such as increases in the Social Security retirement age. With people being encouraged to work as long as possible, how, she wonders, can society can create enough jobs to meet the need, and how can we expect the worn-out elderly, especially manual laborers, to work well into their final years to ease their financial burden.

Jacoby includes affecting anecdotes from her own life to put a human face on the dire medical facts and statistics she recounts. She describes her grandmother, who died in a nursing home, her mind intact, just shy of her 100th birthday; her mother, 89 when the book was written and living in an assisted-living facility, so compromised by osteoporosis that she could hardly turn over in bed; her father, who died a “good” — i.e., non-medicalized — but much-too-young death at age 71 from lung cancer. And she writes movingly about sharing “the long mental deterioration of the person I loved most in the world,” her “lover and best friend,” a lively, intelligent man who was diagnosed with Alzheimer’s and mercifully died from cancer before he sank into a mental black hole.

Jacoby, born in 1945, just outside the baby boom, identifies with the oldest of that cohort in both experience and outlook.  Like a human GPS, she positions herself in a moral universe. She is an atheist, a secularist, a humanist and a liberal, and it’s these attributes that inform the most thought-provoking parts of her book. With ingenuity, she argues against the idea that people grow wiser as they grow older. Surprisingly, she supports research to extend life — even to age 120 — on the humanist grounds that people can choose to do what they want with their money and lives (though such research, she stresses, should not “have a preeminent claim on public resources” or be at the expense of research to eliminate scourges  such as diabetes, cancer and Alzheimer’s). Bravely, she takes on the “helping professions” — and anxious friends and relatives — who try coaxing old people into lives of complacent social conformity, marked by activities such as sing-alongs and bridge games, without allowing that some may prefer to be left alone.

The only jarring note in the book comes from the intemperate language Jacoby uses at times in describing ideas of those on the “right wing”; expressions like “cockamamie,” “weird scenarios” and “shameless” are uncalled for when those ideas are discussed in adequate detail to convey their substance.

Jacoby proffers no magic pill for dealing with old age in America, but she calls for baby boomers to lead the way in forging an intergenerational contract that will recognize the responsibilities of one generation to another. This will require political will and sacrifice from all members of society, and almost certainly increased taxes and some adjustment of benefits.

But the intergenerational contract she envisions extends beyond financial issues to encompass emotional ones as well. Loss of control over their lives is the greatest fear of mentally competent old people, she says. Respecting their desire for autonomy while at the same time insuring that the elderly are relatively safe and secure — they need not be treated as children — is the greatest gift others can give. In the end, and in ways not recognized at the beginning of the book, Never Say Die is life-affirming.

Harriet Douty Dwinell is a writer, editor, memoirist, and former university professor whose writings have appeared in the New Republic, Family Circle, Washingtonian, the Washington Post, and other publications. She is now exploring issues of aging.