HALF a century ago, when Walter Pitkin published his then-daring ''Life Begins at Forty,'' his thesis was derided as shameless hyperbole in many quarters. Those quarters did not include the Brooklyn environs frequented by my maternal great-grandfather: Rabbi Hirsch to his learned contemporaries, ''Zaida'' in the uneasy bosom of his family. Our Zaida came to immigrant Brownsville at 76, plunged headlong into its feisty communal life, and after 20 vigorous years departed, leaving a trail of Talmudic academies, improvised prayer halls (''Murphy's shul,'' a converted tavern, was my favorite), and imperishable memories. His abundant snowy beard and mischievous grin were part of my childhood, as was the afternoon when he gave me an unsolicited golf lesson in my grandmother's garden, turning his cane upside down to demonstrate the art of putting.
My grandmother, emigrating to the New World with a young husband in the late 1880s, had left her widowed father behind in an obscure East European shtetl. Years later, comfortably established in America with her husband, Henry, entrenched in local politics and her family growing, she thought wistfully of her forsaken parent. Would it not be a happy inspiration to share her good fortune, bring him across the sea to a peaceful land where he could live out his twilight years in scholarly serenity? In her mind's eyes, daughter Teresa could see her father transplanted to the sprawling Holtzmann house on Eastern Parkway: sitting in his slippers before the stove, sipping tea from a tall glass, poring over his Hassidic tracts for one last time before shuffling off to bed.
Wheels were set in motion. No less a personage than Secretary of State Elihu Root dispatched a cable to the United States minister in Vienna. And the elders of Rohatyn (pop. 200, quite indistinguishable from the mythical Anatevka of ''Fiddler on the Roof'') were astonished to see two gentlemen in frock coats descend from a limousine. Where could they find Rabbi Hirsch Bornfeld, father-in-law of that good Republican, Henry Holtzmann?
Within minutes, they were pumping the hand of an affable white-bearded patriarch. Blue eyes twinkling merrily, Hirsch Bornfeld stuffed a few books, clothes, and toiletries into a borrowed suitcase, placed his rabbinical certificate carefully on top, and consented graciously to be escorted to Hamburg , where passage to America had been booked for him on the sumptuous Kaiser Wilhelm Grosse.
Word was flashed back to Eastern Parkway, where the family looked forward to greeting a typical Zaida or elderly grandfather: a venerable if not doddering relic, fragile as porcelain, and perhaps fuzzy-minded to boot.
When the great liner docked and the ancient was not found in his cabin, panic coursed through the familial ranks. Gloom deepened - until our Zaida was discovered on the top deck, posing for the Sunday rotogravure with Marcella Sembrich, the Metropolitan Opera soprano. He had been a star passenger, it developed, by virtue of his exotic theological background, delivering a nightly benediction at the captain's table in classical Hebrew.
With a parting bow to Madame Sembrich (she invited him to opening night at the Met, he urged her to catch him at the altar in Brooklyn), Zaida signed a couple of autographs and permitted his relatives to cart him off.
He settled into the room prepared for him, but quickly made it plain that he did not plan to spend much time there. The Saturday morning after his arrival he sallied forth in Prince Albert cutaway, black trousers, and towering stovepipe - summoned, he explained, to preside over a neighborhood bar mitzvah. Within weeks his fame was established to the point where, as Teresa drily observed, ''nobody in Brownsville'' could get married, confirmed, or graduated without benefit of Zaida's baronial wardrobe and courtly manner. The local widows showered him with loaves of fragrant cholleh. Teased about their yearning glances, Zaida shrugged off suggestions of matrimony: ''Why should I be tied down to one woman, when 10 will bake for me?''
He was less dispassionate about politics, having been district postmaster at Rohatyn and - so he claimed - an adviser to the local count. When his grandson Jacob was nominated for Congress as the Bull Moose protege of ex-President Teddy Roosevelt, Zaida appointed himself campaign chairman for the elder-citizens vote , holding forth at street corner rallies on the virtues of reform Republicanism.
As his reputation for wisdom grew, Zaida established a rabbinical Bes Din (House of Judgment) in the summer house of the Holtzmann garden. Why, he demanded, should disputing neighbors get caught up in the complexities of court calendars and legal fees, when with reasonable goodwill a fair compromise was always possible? And what mere statutes of mortal man, varying between New York and Hoboken, could compare with the universal law of the God-given Torah? Zaida dispensed tea, sponge cake, and parables; usually his contestants departed arm in arm, after allocating a joint contribution in praise of the Lord: a stained-glass window for the synagogue, new textbooks for the children's Talmud Torah, or Hebrew school.
Prayer and study were close to Zaida's heart. He would cheerfully consecrate the corner of a grocery store for Sabbath services if no better site was available. But, true to Hassidic tradition, he always laced his piety with humor. He was in his 90s when, dipping into the surf at Coney Island, he lost his bathing suit to a powerful wave. As grandchildren rushed to his rescue, Zaida alone retained his aplomb: ''I'm no worse off than when I came into the world.''
When he passed on at 96, multitudes came to pay tribute. But there were few tears, in acknowledgment of his parting counsel: ''Remember the good times we had together.''
Life begins at 40? Not for Zaida. He needed no renewals, because he had never broken its original continuity. Life was a gift to be celebrated every day, at any age, an occasion for joy in the bounty of the Lord. Life was to be lived.