I am 20 years old and I feel something is wrong with my colon and I have all the symptoms that arise from colon cancer. I read that colonoscopys are given to people over 50 because people my age arent at risk or it's rare to have colon cancer. and I was just wondering what other things are there that have the same symptoms as colon cancer?
No. Polyps don't have any symptoms–although I suppose a grotesquely enormous polyp could obstruct the colon, I have never heard of such a growth. Polyps tend to just be found on a regular colonoscopy and are removed by biopsy in case they are cancerous.
If you are having symptoms that you associate with "colon cancer" it is far more likely that you actually are experiencing another GI issue, perhaps: inflammatory bowel disease (Crohn's disease or ulcerative colitis), irritable bowel syndrome, or diverticulosis. Also, fructose and glucose intolerance (coeliac disease) can present with extremely unpleasant symptoms (far worse than lactose intolerance).
All of the above (except for fructose intolerance) are diagnosed with colonoscopy, which will rule out colon cancer. Accordingly, I would call a physician and see a gastroenterologist so you can sleep easier! Except for the most severe cases, most of these can be well managed with oral medications or dietary changes.
All of the above diseases can be characterized (depending on disease severity) by any mixture of the following symptoms: loose stools, abdominal cramping, blood in the stools, urgency, fecal incontinence, gas, bloating, noted inabilities to eat certain foods (i.e. most IBD patients get diarrhea from corn or pain from whole nuts), rectal pain, fatigue, anemia.
Try reading about the inflammatory bowel diseases (IBD) and see if this sounds like what you may have:
ccfa.org/info/about/crohns
ccfa.org/info/about/ucp
Although a colonoscopy probably sounds really awful to you, as someone who works with them on a regular basis and sees people who need to have them regularly, I assure you that it is far better to have a colonoscopy than to live with chronically active bowel problems.