* 33-year-old Australian great calls time * Caps career with six Olympic medals and 11 world titles (Adds quotes, details, byline) By Ian Ransom MELBOURNE, Oct 16 (Reuters) - Australia's track cycling queen Anna Meares announced her retirement on Sunday, two months after grabbing her sixth Olympic medal to cap a career defined by courage and sacrifice. The twice Olympic champion, who won 11 world titles and bore her nation's flag at Rio, mulled bowing out at the 2018 Commonwealth Games in her home state of Queensland but said the physical toll extracted by 22 years of competition had helped make up her mind. More...