When Jane Southwick entered the world a century ago, her parents thought their family had just welcomed one baby. Then the doctor realized there was another child on the way. Moments later, her twin brother, Bill Abbott, arrived, turning a routine birth in Hawaii into a family legend that would span 10 decades.

Raised by Royal Abbott, a Navy man stationed in Hawaii, and Loreen, a choir director, the twins spent their early years moving between Hawaii, the U.S. mainland and Canada before settling into high school life in Long Beach and Oakland. Longevity, it turns out, was part of the family fabric. Both parents lived into their mid-90s, and their older brother Richard lived to nearly 103, anchoring a sprawling clan of children, grandchildren and great-grandchildren who still gather in California’s Bay Area.

Jane built a life rooted in education and family. After earning a degree in child development, she taught nursery school and raised five children with her husband, Ernie, whom she met at UC Berkeley after her mother suggested she catch a ride with the young man who owned a Studebaker. She later turned family stories into history, publishing a book about her Civil War–era great-grandfather, drawing on memories and research.

Her century has not been without hardship. Jane survived breast cancer, major surgery and ongoing pulmonary problems. Bill, who lives in nearby Pleasanton, remained robust until a heart attack about a decade ago led to stents and ongoing kidney issues. Both credit their niece Linda and Jane’s daughter Nancy, who moved in to care for her mother and now helps both twins manage daily life and medical appointments.

Doctors marvel at their resilience. One cardiologist told Jane she has “a 60-year-old heart.” Bill’s physician is more wry, telling him that at 100, his heart is “doing just as good as it can.”

Asked for their secret to longevity, the twins point first to family and then to lifestyle. They grew up in a home without smoking or drinking, stayed active, and leaned on strong medical care and one another. Bill, a former high school athlete, swam in the ocean, served aboard the battleship USS California in World War II, then flew patrol planes in the Navy Reserve before a long career as an engineer.

Travel, too, kept them young. After Bill’s wife Patricia and their brother Richard died, the siblings and their extended family spent about 15 years exploring together, from Hawaii to Italy to the American West, collecting stories of lost passports, recovered wallets and shared glasses of wine.

Now, the adventures are closer to home. Each year, Jane’s house fills with relatives for Christmas and milestone celebrations, including the twins’ 100th birthday. Surrounded by generations who have watched them weather wars, illness and loss, Jane and Bill insist they still feel like “kids” at heart, living proof that long life is as much about connection and attitude as it is about genes.