It's simple. Get screened.
Father Fangman discovered he had colon cancer only after turning 50 and getting the recommended screening - and he admits he put it off longer than he should have because of his busy schedule. He was experiencing no symptoms at the time of his diagnosis.
While more and more young people are being diagnosed, the current recommendation is that screenings should begin at age 50 if there is no previous family history of colon cancer. The risk of colorectal cancer increases as people get older, and the majority of colorectal cancers occur in people older than 50.