In 2012, Ashton Applewhite was invited to speak at a performance festival whose theme was so scary that friends of the organizer warned she would lose all her subscribers. The topic? Aging. As it turned out, the naysayers were wrong. Subscriptions to the festival tripled, confirming what Applewhite already knew from her work as a public speaker, performer and the author of “This Chair Rocks,” an anti-ageist blog.

She recently published a book of the same name, a self-described manifesto that she hopes will transform the way Americans think of aging in the same way “The Feminine Mystique” helped catalyze the women’s movement a half-century ago.

The goal, she admits, is “absurdly ambitious.” But Applewhite, who travels the country trying to reverse negative stereotypes about growing old, believes America’s anti-ageism moment has arrived. “People are hungry for a narrative that rings true to our experience of growing older,” she said. While much of American society now considers it unacceptable to be openly sexist, racist or homophobic, “old people are still fair game.”

Applewhite rails against greeting cards that make fun of saggy skin and lost keys — the view of aging as nothing but decline. “Why should I accept the notion that the present-day me is inferior to the younger me?” Born in 1952 in the middle of the Baby Boom generation, the former book editor said she was as terrified as anyone of old age. But a project about people over 80 who still worked spurred her to rethink common stereotypes — that old people were weak, boring or incompetent — and to dig more deeply. “I started learning about longevity, and everything I heard was so much more positive than the common wisdom.”

For instance, there is a U-curve for happiness — it declines in young adulthood and increases for people over 50. Or that only 4 percent of people over 65 live in nursing homes. “The scary stuff about aging is real, but our fears are hugely out of proportion.” She calls it a prejudice against our future selves, and like any prejudice, it is mired in ignorance. But it is one she herself has struggled against. “I know in hindsight that I started writing because I was afraid of getting old,” she said. With her angular features and stylish mass of brown curls, her appearance does not scream, “63-year-old grandmother.” But that is her point: The older a person gets, the less easy it is to define that person by looking at chronological age.

Looking back, she said, “I miss my cartilage, but I really don’t miss anything else.” She is no stranger to writing about herself (her first book, about women who end their marriages, came in the wake of her own divorce). After raising four children together, she and her longtime partner moved 10 years ago from Manhattan to Williamsburg, Brooklyn — a magnet for young people — and, perhaps not coincidentally, became passionate about ageism. The movement’s time has come, she says, in part because baby boomers, who begin turning 70 this year, can no longer hide from the fact that they are getting old. “It turns out that, no matter how much kale I eat, no matter how many memory exercises I do, I’m actually not going to dodge this whole aging thing, the same as every mortal in the world.”

The book explores the origins of our cultural biases against growing old, examines the role of the “medical-industrial complex” in perpetuating stigmas about old age and offers tips on how to change one’s attitude about aging.

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“The field needed a public intellectual, and Ashton, it turned out, was really great at it,” said Margaret Gullette, author of “Agewise, Fighting the New Ageism in America,” and a mentor to Applewhite. “She’s a dynamic speaker; she has a succinct story about how she changed her thinking about aging, and she is charmed to be happier about getting older.”

Applewhite wants others to be charmed as well. One way to get there, she says, is to simply spend time with people of different generations. “It’s shocking how age-segregated American society is,” she says. “Nothing changes if we stay in our silos, and one of the really, really important things about living in society is having friends of all ages. It connects people empathetically, and that’s critically important.”

A second Applewhite blog — “Yo, Is This Ageist?” — invites people to submit examples of ageism in daily life. Some recent examples: an ad offering to “make an Android easy enough for even Grandma to use” or a list of “boring cities,” so determined by the percentage of old residents. She encourages people to speak up when they see such examples. If they don’t, she warns, they will one day find themselves on the wrong side of history.

“You can aspire to stay healthy, and you should,” she said. “But aspiring to youth is self-destructive and futile. You cannot stay young; it’s a dumb goal.”