By Liz O'Neil

When "The Joy of Being Single" was published, author Allia Zobel, lean, leggy, attractive, lounged in the window of a Fifth Avenue bookstore, a tray of forbidden fattening food at her side, a fuzzy stuffed cat at her feet. Zobel was 40-something, promoting her first published "little book." Illustrated by New Yorker artist Roz Chast, "The Joy of Being Single" brought a lot of laughs, sold well. That was in 1992.

Time passes. Among her newspaper columns and freelance articles, Zobel wrote four more small "volumes." These she devoted to the vagaries of living with a cat or two, wry humor bought by a myriad of cat people and their feline-loving friends.

Than along came Desmond Finbarr Nolan, computer analyst from Ireland, sweeping the 40-something author off her feet, into marriage. It mattered not that Nolan was uncertain of his bride's accurate age; the wedding was written about in the New York Times' Style Section.

Zobel soon sat down and wrote another book of one-liners titled "Younger Men are Better than Retin-A."

Today one finds Allia Zobel, fresh-faced, lithe, lively as ever, propelled by vegetables, exercise, a frisky mind. She speaks now of her latest amusing little book, "The Joy of Being 50 plus." And again adding laughs are artist Roz Chast's kind-of-frumpy, surprised women, their expressions echoing our own.

"Indulge your eccentricities," Zobel has quipped, advising 50-plus women. "Take naps with your cats. Ditch the mini-skirts and tight sweaters in favor of long skirts, 'big' jewelry and Birkenstocks. Make love like a bunny without a care. Buy birthday candles in bulk. Note that your kids are starting to be good to you."

Alliz Zobel, now earnest, writes, "It's not age but attitude that counts. So, since you're going to turn 50 anyway (some people more than once), it makes more sense to treat the occasion as a milestone." She feels that 50 is the perfect age to quit trying to be perfect and to stop taking oneself so seriously. The prolonged angst one suffers when young and disappointed, at middle age lasts a week.maybe two.

"Truth is, there's plenty of joy in being 50 -- if you're open to it. It's the perfect time for folks to do whatever it is they have in their hearts to do - or not to do. After all, anyone who's lived half a century has earned the right." Allia Zobel laughs, "Think of it, no one can tell you to grow up any more."

The possibility of new adventures brings on a surge of freedom. When we're born we don't know anything. If 50 is a chance to be reborn, with 50 years of knowledge behind us, it should be an opportunity to create the kind of life we want.

Zobel as philosopher says, "Actually, we need middle age. If you suddenly woke up one morning and found you'd gone from youth to old age, you'd suffer whiplash. Middle-age, 50-plus, helps make that transition. It gives you the time to develop the right attitude!"

Allia Zobel, with a successful publishing track record, no longer needs a shop window tableau promotion. Book signings, her enthusiasm and belief in her books, propel interest and sales. Her attention is turned today to religious books for kids, another humorous cat book and, on the back burner, a new one-liner.

("The Joy of Being 50 plus" (Workman Publishing) is available in major bookstores and online.)

Author's note: Our male population seems more stolid about turning 50, though one 52-year-old entrepreneur threatened to initiate the ALMA Club. "Stands for 'At Last, Middle Age'," he says. "Any acronym is okay after half-a-century being called a Baby-Boomer!"