I wondered if anyone could give me the symptoms of colon cancer, a little detail on them too. could i have it at 18?

Usually None: Colon cancer frequently will develop without symptoms until rather advanced. It would be exceedingly unusual for an 18 yr old to develop it in the absence or an underlying condition like hereditary polyposis or peutz–jeghers syndrome. Common symptoms would include change of bowel movements, blood in the stools (often not apparent without testing). Some cancers will present with bowel perforation!