A virgin at 23, male silverback makes mild debut at S.F. Zoo. Twenty-three years of sexual rejection might have been too much. The San Francisco Zoo's new male gorilla, successor to the late and virile Kubi, is finally spending quality time with the public and his four female companions -- and so far, the public seems more interesting. "Sometimes the libido doesn't kick in right away," said longtime gorilla keeper Mary Kerr. Zoo spokeswoman Nancy Chan put it more bluntly. "He's a wimp," she said. The ape's manhood, and even his name, are still question marks. Born at Ohio's Columbus...