ON THE last day of April this year, my great uncle, Donato Calandriello, turned a healthy, lucid 100. I, having entered my 30th year, am prone to think now about such things as longevity and how to achieve it. So I asked my grandmother what Zio Duce (an Italian idiom pronounced tsee-dooch and meaning "Uncle Dan") eats. After all, her sister, Adoralta, was married to him for some 70 years.

"Does he drink coffee?" I asked. A year ago, I'd given up coffee.

"Oh, sure," said my grandmother, 92 and robust herself.

"How many cups?"

"One cup."

"For breakfast?"

"Yes."

Good. We were getting somewhere. This was no 12-cup-a-day man.

"And what else for breakfast?"

"A jigger of gin."

"And?" I asked weakly.

"And about a quart of red wine through the day."

So much for yogurt.

For reasons Italian, I'd never met Zio Duce, even though I'd lived not far from him for my first 17 years. Still, I made sure not to miss his centennial. I wanted to see him for myself and watch and listen for his secrets. The celebration was held on a cool, sunny Sunday at his home in Rye, New York.

I found Zio Duce, shortly after noon, at his kitchen table in the sparsely furnished house he built himself of stones and mortar in 1917. There were other people in the room, and I did not pick him out immediately as the 100-year-old. His eyes, though failing, were alert and bright, and rested on mine with patient curiosity. He sat so erect, it was not clear that his back was touching the chair. His white hair stood out like a crown. Meticulously wiping red sauce with a torn piece of rough bread, he was finishing his lunch of lasagna.

By his plate was a small glass of red wine. The bottle beside it was old, with the label scatched off. When, with an unwavering hand, he poured another glass for himself, I saw sediment floating.

My grandmother had told me he used to make his own wine from the grapes he grew and would chill it in his well. I asked in a loud voice where he'd gotten the wine he was drinking today, but, it was immediately apparent, there was no need to shout.

"It's ten years old," he said proudly, his words steady and clear. "Someone brought it to me as a present."

I asked who had make his lunch.

"My daughter-in-law."

His late son Murray's wife, Carmela, is a quick, slender woman who lives in the apartment upstairs. When she came in, she slipped a bright blue sweater on the man she calls "Pop." Then she helped him with his windbreaker, perfunctorily handed him his hat and disappeared.

Sweat stains swirled around the band of the ancient hat. Clearly it belonged to a man who had made his living as a gardener, a worker in salt mines, a man who retired at 80. Zio Duce put on the hat and headed outside.

He makes his way with a walker now, an encumbrance he's been forced to use since he fell and broke his hip shoveling snow--at age 97.

Past his cold-frame set against the house, where, I learned, his tomato and pepper plants were growing, he went around to the sloping side yard to greet a burgeoning crowd of family and neighbors.

A chair was set up for him near my grandmother and other relatives, all of them bundled in coats and scarves against the spring wind; but Zio Duce waved the fuss away and walked further up the hill.

"He wants to go where he always sits," my Aunt Mary said.

His chair was put against an aging tool shed whose lock was a pair of scissors dropped through the latch. Here he sat, the sun in his face, as people came to wish him "Happy Birthday," give him bottles of gin and wine, and ask about the old well, his grapes, his garden.

From this seat he can, as he does daily, literally watch the garden grow. Its rich black soil had been spaded, and Zio Duce had planted scallions already, leaning over his walker to do it. My uncle told me Zio Duce shelters himself inside the shed in cooler weather, looking outdoors. In winter, he sits at the window in his bedroom; he can see the garden from there, too.

"He loves everything from the garden," my grandmother said--both raw in salads and cooked. Greens, particularly: escarole, cabbage, swiss chard, dandelions. Recently she cooked him greens the way he likes them, using cabbage, and brought them to him as gift: COOKED GREENS (4 servings) 1 pound smoked ham hocks 1 pound cabbage leaves

Boil the smoked ham hocks until the meat falls off the bone--about 2 hours. Steam cabbage leaves. Combine the meat and the cabbage; simmer some more.

Carmela told me Zio Duce is no vegetarian. "He loves his meats, loves capons, veal chops, chicken wings. He's not a macaroni eater, really. He likes the meat from the sauce."

In the old days, she said, one thing he loved especially was a lamb's head baked with parmesan cheese, flavored bread crumbs and "a drop" of oil, at Easter time. Another of his favorite things is an orange salad. ORANGE SALAD (1 serving) 1 orange, sectioned A few cloves garlic, pressed A drop of oil Pinch of salt

Toss the orange sections with the garlic. Add oil and salt.

Shallots are another favorite dish, she said. She serves it to him this way: SAUTEED SHALLOTS (1 serving) Handful of shallots, peeled 1 tablespoon butter or oil Salt

Peel "a handful" of shallots; boil until soft. Saute' in a tablespoon or less of butter or oil. Add salt.

"His big meal of the day is at noon, his dinner," Carmela said, rushing off to tend to her guests, who were feasting on grilled sausage, marinated mushrooms, pasta dishes of every delectable description, all of it brought by the family and neighbors.

When the crowd had swelled to perhaps 200, the elected officials arrived. They all spoke too loudly to Zio Duce at first, much too close to his face, pronouncing their t's and d's very distinctly.

Zio Duce regaled them with stories of his past. He is obviously proud of his memory, and, remarkably, never dropped the thread of his tale, despite numerous interruptions.

He said he got his first job in America in New York City on the day he arrived from Barillo (near Potenza, in the south of Italy), at age 20. The job was in "a saloon," where every morning he'd cook soup. He would go to "the meat shop" and get "15 to 20 pounds" of meat; add parsnips, turnips, carrots, onions, "a couple of handfuls" of flour and "a very few" tomatoes.

I asked how long he cooked it, but before he could answer Carmela came running up the hill, trailed by a short, eager-faced, red-haired man. "Here's another politician, Pop," she said.

A state assemblyman, he started to read a proclamation signed by the governor.

"He'll vote for you, John. Don't worry about it," Carmela cut in.

"You don't have a public address system here, do you?" the mayor asked.

While he went off to read his speech from the bandstand, Rep. Richard Ottinger (D-N.Y.), kneeling, promised a letter from President Reagan.

Zio Duce, gracious, tireless (he sat outside for close to four hours, going in only after the sun had moved around the house), with a gardener's patience and a simple man's uncomplicated tastes, listened politely.