 He turned professional when he was 16 and would later say that the only regret in his career was giving up his amateur status before the 1948 Summer Olympics.In 1949, at the age of 18, Lumsdon won the world marathon championship in Toronto, defeating 46 competitors in the annual 15-mile race at the Canadian National Exhibition.He won $6,300—$5,500 for winning the race and $800 for leading all laps and swimming the fastest lap.