Why are you getting this done at your age? Do you have a hereditary colon cancer syndrome that runs in your family? There are two of those- Lynch Syndrome and FAP. If you have the latter condition, a colonoscopy at your age makes sense, and is a necessary part of your care, because eventually you're going to have to have your colon removed. And if you have the first condition, Lynch Syndrome, then it's imperative that you start screening for colon cancer as early as possible, in order to have the best chance of detecting and treating the disease.
But if you don't have either of these two conditions, then you're WAY TOO YOUNG to be undergoing this procedure.