Gus Kao, who just turned 98, has led the Qigong exercise class at Rossmoor for a quarter of a century. But, he says, a bout with a stomach ulcer earlier this year has sapped his energy and he’s passed the mantle to other instructors. Peter Li, president of the Chinese-American Association of Rossmoor (CAAR), which sponsors the class, describes Kao as “one of the great treasures of our club.”