At age 74, America's longest-serving astronaut is retiring. John Young joined NASA when Kennedy was president. His first space flight was in 1965 when he piloted the first manned Gemini mission. Later he made two trips to the moon -- orbiting during a 1969 flight and then walking on the lunar surface during a mission in 1972. Nine years later he commanded the very first space shuttle flight, the debut of "Columbia." His final space mission came in 1983 when he again commanded Columbia. December 31st will be his last day on the job. NASA associate administrator William Readdy says Young has set the gold standard for asking really tough questions. Johnson Space Center Director Jefferson Howell Junior calls him "the astronaut's astronaut, a hero among heroes who fly in space."