How unlikely would it be that a person in their late 20s would have colorectal cancer?

Rare: But it does happen and if strong family history and symptoms, blood in stools, etc., get it checked out.

Still low likelihood: Recent studies showed that among people ages 20 to 49, incidence rates of colorectal cancer increased 1.5 percent per year in men and 1.6 percent per year in women. However, among people ages 20 to 29, incidence rates rose by 5.2% per year in men and 5.6% per year in women. The current rates in white male and female are 10.2 and 8.8 cases, respectively, for every 100, 000 people. Still a low rate.

Rare: This would almost always be due to a hereditary form of cancer and is rare but not unheard of.