I'm 30 and my doctor said that it should be a part of my annual physical. Sporadic cancers have been seen in people in their 20s. However, routine screenings are recommended at age 50, or earlier if there is a strong family history of colorectal cancer. It never hurts to start earlier. Patients who are immobilized in the hospital have near-complete shutdown of bowel function.
Polyps are abnormal growth which occur on the inner lining of the colon.
Most, if not all, cancers begin as polyps. If allowed to progress, cancer will develop within 5 years. This is why it's important to get screened. In Africa, who are basically vegetarians, have an extremely low incidence of colorectal cancer. Whereas, industrialized countries with higher dietary fat intake have higher incidences.