The stock market is imploding, Europe is on the brink, and, if the doomsayers are to be believed, we could be headed for a double-dip recession.

None of that worries Irving Kahn, perhaps the world’s oldest working investment banker. “There are a lot of opportunities out there, and one shouldn’t complain, unless you don’t have good health,” says Kahn. At 105, he might well be the last man on earth who can speak authoritatively on both longevity and making money amid a historic market meltdown. In 1928, at the age of 23, he went to work on Wall Street as a stock analyst and brokerage clerk. By the tail end of the Great Depression, in 1939, he’d made enough money in the market to move his wife and two children out of public housing and into their own house in the suburbs.

Kahn is still in the game, waking every morning at 7 and going to work as chairman of Kahn Brothers, the small family investment firm he founded in 1978. Until a few years ago, he took the bus or walked the 20 blocks from his Upper East Side home to his midtown office. “For a 105-year-old guy, it’s pretty remarkable,” says Thomas Kahn, Irving’s 68-year-old son and the company’s president. “I get tired just thinking about it.”

Perhaps his closest rival for the title of oldest person working in the securities industry was the financier Roy Neuberger, who passed away in 2010 at the age of 107. But Neuberger had retired at 99. Two of Kahn’s older sons, both in their mid-70s, have likewise retired.

Small and gnomish, Kahn counsels patience in hard times as he holds forth on market distortions and the roots of economic unrest, which he pins on “a bunch of gamblers going crazy on the floor of the exchange.” “Wall Street,” he adds, “has always been a very poor judge of value.”

The depths of the Depression turned out to be a useful time to learn that lesson. At Columbia Business School, Kahn served as an assistant to economist Benjamin Graham, the value-investing guru whose principles of caution and defensive investing inspired a cadre of disciples that includes Warren Buffett. It’s an investment strategy born of the beating Graham had taken in '29, and Kahn adopted it as his own. “I stopped wasting time on what people claimed a stock was worth and started looking at the numbers,” he says. “This may surprise you, but there were a large number of valuable buys during the Depression.”

Then and now, he says, the smart money was on companies with sound fundamentals. “You always had a long list of what I’d call legitimate businesses,” he says—the ones that produced food, clothing, and other essentials. “Everybody still wanted a clean shirt. They wanted to buy Procter & Gamble.” A science buff, Kahn also grew adept at spotting the long-term potential of emerging technologies and new industries. In the 1930s, that meant radio and movies, both of which boomed despite the downturn. Today he’s apt to talk up environmental and energy startups. “You have to have a certain amount of cultural interest in technology to be early in the field,” he says.

Life for a Depression-era Wall Streeter was markedly frugal by current standards: Kahn and his wife, Ruth, enjoyed a penthouse apartment in public housing—the Knickerbocker Village complex on Manhattan’s Lower East Side. “My kids were brought up as if they had a wealthy father, which they didn’t.” He’d walk home for lunch, to save money on restaurants. Kahn’s fortunes improved as the Depression wore on: by 1939 he was doing well enough to buy a house in Belle Harbor, Queens, and he later prospered as the director of several companies, including the Grand Union supermarket chain.

But his habits have remained exceedingly modest. “Irving’s a funny guy,” Thomas Kahn says. “He doesn’t play golf, there’s no weekend house, no country-club membership.” For years he ate the same dish—chopped steak, rare—at the same time-worn French restaurant, Le Veau d’Or, on the Upper East Side. He traveled only reluctantly, at the urging of his wife, and would haul stacks of annual reports to read on Caribbean vacations. Ruth died in 1996, after 65 years of marriage, and Wall Street became his main companion. “I couldn’t find another person or occupation that had as much interest for me as economics,” he says.

For the past several years, Kahn’s longevity has been the subject of scientific inquiry: he’s participating in a study of centenarians at the Albert Einstein College of Medicine in the Bronx, by geneticist Nir Barzilai. Barzilai hypothesizes that Kahn’s extraordinarily high amounts of “good” HDL cholesterol are exerting some protective effect, warding off age-related infirmities. It just might be luck, a genetic gift that he shares with two centenarian siblings, including an older sister of 109 and a younger brother of 101.

Thomas Kahn seems convinced that the market itself is keeping his father alive. Indeed, watching indexes gyrate offers the elder Kahn endless diversion. “I get a kick out of seeing who’s going to come out ahead in this race,” he says.

This is one of the gifts of age, scientists say—the ability to focus on the bright side of things, a talent that Kahn displays in abundance. If you can believe him, happy days will be here again.

“I’m a great bull on American democracy,” he says. “If you give me a long leash on this dog, I can hold him at bay.”

If this downturn culminates in an actual depression, says Kahn, it will end more quickly than the one he endured as a young man, because technology will somehow turn the economy around. “Sometimes favorable surprises come out of the blue.”