(CNN) -- As Dorrie Aber-Noyek enters the cafeteria at Memorial Regional Hospital in Hollywood, Florida, the staff bursts into a round of "Happy Birthday."
It's her 104th birthday, and the chef has made one of her favorite dishes, chicken Alfredo. Hugs are given, congratulations offered and then the hospital's CEO, Zeff Ross, cuts the party short.
"At one o'clock, Dorrie has to go to work!" Ross tells the crowd.
At age 104, Aber-Noyek, who has volunteered at Memorial for 37 years, still walks the halls to deliver the mail -- and it's a big hospital.
"I can slow down for you if you want," she tells CNN photojournalist Jerry Simonson as he tries to keep up with her as she rolls her cart down the corridor.
Aber-Noyek, who turned 104 in February, lives by herself, and other than a bit of arthritis and slightly imperfect vision and hearing, she says she's in perfect health. When asked for her secret to such a long life, she shrugs her shoulders.
It's not her diet -- Alfredo sauce certainly isn't low in fat, and she eats a piece of cake or a cookie (or two) every day (her favorite is chocolate chip). It's not her physical activity -- while she's always enjoyed walking, she never belonged to a gym or worked out regularly.
A new study suggests Aber-Noyek is typical of what scientists call "super agers." The research, published in The Journal of the American Geriatrics Society, found that people who live to be 95 or older do not tend to have lived a healthier lifestyle than others who died earlier.
"As a group, the centenarians were really very bad," says Dr. Nir Barzilai, director of the Institute for Aging Research at the Albert Einstein College of Medicine, and senior author of the study.
Barzilai asked 477 healthy Ashkenazi Jews between the ages of 95 and 112 about their lifestyle habits when they were 70 years old. More than 40% said they were obese or overweight, about 35% smoked and very few exercised. Their habits were no different from those of a comparison group of people from the general population.
"What this shows is that it really is the genes that helped the centenarians," he says.
Research done by Barzilai and others has shown that centenarians often have a gene associated with a higher level of HDL, which is the good kind of cholesterol. They also often have genes that seem to protect against cardiovascular disease and Alzheimer's disease.
He warns that this doesn't mean everyone can smoke and eat poorly and expect to live to 100.
"The centenarians have longevity genes that protect them, so it doesn't matter what they do," he says. "But for the majority of us who don't have those genes, it really does matter. We really do need to listen to what the doctor tells us."
Other research has shown that centenarians tend to have strong ties to the community and are less likely to be depressed.
Both theories -- the nature and the nurture -- seem to fit Aber-Noyek. Her mother lived to 99, and she also has strong ties to the people around her.
"I'm enjoying life," she says. "I love people. I'm very interested in them. I love to talk to them and ask them questions about themselves."
She's as surprised by her longevity as anyone else.
"I never had the ambition to get to such an age. It just happened. Sometimes I think, 'How in the world did I get here?'" she says.