The U.S. Preventive Services Task Force and American College of Gastroenterology both recommend the colon cancer screening guidelines should start colon cancer screening at age 50.  They also recommend continued surveillance until at least age 75 depending on other health factors.  If there are other risk factors involved like family history of colon cancer or precancerous polyps (adenoma), personal history of other types of cancer or a hereditary condition that you may have that is associated with increased colon cancer risk, then you would be screened at a younger age.  Unexplained rectal bleeding at most any age should be evaluated as well.  If you have specific questions as to when you should be screened, please contact me at my San Antonio gastroenterology clinic.