Colonoscopy is good preventative medicine for everybody over the age of 50. A video was posted yesterday on colon cancer metastatic to the liver. Although this is treatable, metastatic colon cancer is a miserable condition, markedly lowering quality of life. You are much better off preventing colon cancer then having to deal with it, and in this sense, colonoscopy is a very good trade off.
Colonoscopy is no fun. You have to modify your diet well in advance, and take a magnesium citrate clean out in order to get rid of fecal matter that would prevent proper visualization of your colon. You should get your first colonoscopy at age 50 or earlier depending upon your family history of polyps, colon cancer, and other bowel problems.
In my own case, I had a number of colonoscopies, and nothing serious was discovered. I still think it is a very good idea. Although I never had a colon polyp or cancer discovered, I have recently, at the age of 89, developed bladder cancer of the slowly progressive and non-invasive kind.
The thought occurred to me that getting regular cystoscopies might catch bladder cancer at an earlier stage. I was told by an authoritative Physician that this has previously been tried and not proven to be useful. I also recommend going into a dermatologist regularly to remove actinic keratoses, which have the capability of developing into cancer. I believe you cannot be too vigorous with preventative therapy.
Interestingly, good sleep, diet and exercise are recommended in the prevention of colon cancer. Please refer to the mayo clinic article on colonoscopy for more information.