Normally the standard of care in America is that people begin having routine colonoscopies at 50 and after (frequency determined by the physician according to initial findings) unless there's another disease or condition that merits the procedure earlier. A colonoscopy is very definitely a way that they can look in people's lower intestines for Crohn's ulcerations or absesses or old scarring. People with a definite family history of colon cancer or familial polyposis generally are told to have their first colonoscopy when they're 10 years younger than the age that their parent/sibling with the disease was first diagnosed, so there are plenty of people out and about who've had the procedure before the age of 50.

I haven't gotten to the age where they're part of my routine care yet, but my husband and parents have had it done and say it's not bad at all.