Woodacre gained its newest centenarian last weekend: Ruth Jane Benz, born Oct. 28, 1923, in Porterville. She celebrated a century of life with friends and relatives at the San Geronimo Valley Community Center on Saturday. A painter, musician and dedicated Warriors and 49ers fan, Ms. Benz has kept her sharp wit and spry form. From her New York Times Sunday crossword to strolls around town with her grandson, she shows no sign of slowing down.…