Her birthday was June 5, and she celebrated among friends and family by enjoying chocolate bars printed with a portrait of her at 20.
"I don't know how I ever got to be 100, I never did anything right. I don't exercise and I don't drink milk, I don't drink water, I don't eat vegetables but I think whatever I'm doing works for me," Headley said, adding that she probably has good genes.
Headley remains in good health and her mind is sharp; she said she can easily recall incidents from her childhood but has difficulty remembering more recent events. She was a resident of Orchard Way in Pleasanton for over 30 years, and has lived at Villa San Ramon for 12 years.
"When I moved here there was just one traffic light on Hopyard Road. It was barn country when we moved here, it's really grown tremendously," she said.
Headley spent the first half of her life in Pittsfield, Mass., near the New York border. The only child of Florence and Arthur Clark, a violist who ran an orchestra and taught piano and violin lessons, Headley said she was very close with her mother and greatly enjoyed accompanying her father when his orchestra performed at dances.
The centenarian still enjoys music and sings karaoke, often harmonizing with entertainers that come to the Villa. Headley believes participating in events in her community helps keep her vibrant.
"I'm upbeat and I enjoy it here. I enter into things and I do things," she said. "They always used to say, if a bus leaves the villa, Marge is on it. I think positive and keep busy."
Headley kept busy well beyond retirement, working at the U.S. Bank, formerly Pleasanton Bank, for 25 years until she was 73. In addition to knowing "where every penny was," Headley said she knew many Pleasanton residents.
When she had vacation time, Headley and her husband, Fran, would travel the world. Over the course of their 47-year marriage, the two traveled to Guatemala, the Greek Islands, France and the South Pacific. The Headleys were also hooked on cruises.
"I love seeing things, meeting new people. The world is such a beautiful place and you have such little time to see all the beauty, all the flowers. It's exciting to see the places I studied about," she said. "I always did everything. I never did anything really, really well, but I tried everything. I even rode a camel in Egypt, I would never forgive myself if I didn't do it."
Headley's fondest memories are of attending Middlebury College in Vermont, where she graduated in 1935 with a degree in French and Latin.
"Because I was an only child, having girls to be with and room with was heavenly," Headley said, adding that she and her friends enjoyed eating fresh maple syrup directly from trees.
Headley didn't want to sit around after graduation and because there weren't many teaching jobs during the Depression, she took a position with General Electric in her home state. Five years later, she met her husband and the two wed in 1941. Headley stayed in Massachusetts with their young children, Phillip and Don (now 70 and 67), while Fran, an electrical engineer, worked on the atomic bomb in New Mexico.
Fran retired from G.E. and took a job with Lawrence Livermore National Laboratory in the late '60s. Headley said it took her about five years to get used to the "atmosphere and karma" of California, not to mention having to drive everywhere. Headley owned a Cadillac Eldorado for many years and enjoyed driving, much like her father, who owned four cars.
Headley will experience a new Californian atmosphere shortly as she prepares to move near her family in San Diego. With help from her son, she is packing a century's worth of clothing and knickknacks, along with her 2-year-old Parakeet Sammy, for the next leg of her journey.
"I love anything pretty. My husband used to say I was born a princess," Headley said, laughing. "I have quite a lot of clothes. I enjoy mix and matching colors, I always liked clothes and purses. In 100 years I've accumulated a lot of them."
As style has evolved over the course of a century, so has Headley's perception of society. The world has changed, and not for the better, because of violence, she said.
"The world's entirely different, has different ideas. They think it's OK to have a gun in your pocket, that it's OK to shoot people. And I think it's due to the wars that we've been having," Headley said. "It's just a different world than I grew up in, certainly. We never had locked doors, and we played out in the dusk, the evening and never worried."
Regardless of her less-than-sunny view of the state of the world, Headley said her secret to longevity is maintaining a positive attitude. She also advises doing everything in moderation -- except eating vegetables, of course.