Young people have always had cancer at some rate, which is why anecdotes here are not particularly indicative. However rare and tragic, it's not unheard of.
That said, the pop media (of which Scientific American is part) routinely conflates rates of diagnosis with rates of late-stage cancer, even though they're very different, and there's a discrepancy between them. I don't know about colon cancer in particular, but I know that it's been a long-term trend in many different cancers -- for example (iirc) skin cancer -- that people are getting diagnosed far more often, but death rates due to the illness are essentially constant.
This tells you either that we're getting worse at treating what we diagnose, or more plausibly, that we're not detecting things that would lead to death.
That said, the pop media (of which Scientific American is part) routinely conflates rates of diagnosis with rates of late-stage cancer, even though they're very different, and there's a discrepancy between them. I don't know about colon cancer in particular, but I know that it's been a long-term trend in many different cancers -- for example (iirc) skin cancer -- that people are getting diagnosed far more often, but death rates due to the illness are essentially constant.
This tells you either that we're getting worse at treating what we diagnose, or more plausibly, that we're not detecting things that would lead to death.