From a 2/28/2017 New York Times article: https://www.nytimes.com/2017/02/28/well ... hone-share
"...adults ages 20 to 39, colon cancer rates have increased by 1 percent to 2.4 percent a year since the mid 1980s, while rates declined overall among those 55 and older. Rates among adults 40 to 54 increased by 0.5 percent to 1.3 percent a year since the mid-1990s.
Rectal cancer incidence rates among adults in their 20s increased even more sharply, rising by 3.2 percent a year from 1974 to 2013. And while rectal cancer rates have declined overall among people 55 and older since 1974, rates in people 50 to 54 increased between 1989-90 and 2012-13. By 2012-13, nearly 30 percent of all rectal cancers were being diagnosed in people under age 55, compared with 15 percent of all rectal cancers being found in this age group in 1989-90..."