This site was started for people diagnosed under age 50. You will find the highest ratio of those dx'd before age 50 right here, compared to anywhere else. If you look at signatures, most of us do have our age at dx, and our staging in our signature. So even if people don't post to your thread, you can still see many dx'd under 50 if you check signatures on any posts you read. There are some people on this site dx'd after age 50 because there is no strict rule, but the original intent was support for those dealing with a bit different situation having CRC before age 50, with issues that many older people don't have - careers and financially in a position they have to work (vs older and likely retired, or at least with more savings and less expenses), young children at home (vs grown children), or worrying about fertility issues because they don't have children yet, or wanted more, etc.
Also, you'll run across a lot of younger people with cancer on the Internet, compared to the "regular" world. The older population is less likely to use the Internet, and even less likely to visit cancer sites even if they do go online.
You are correct about people being diagnosed at younger ages with CRC. While the rate of CRC dx for those over age 50 is actually dropping (due to screening), the rate for those in the 20's, 30's, and 40's is climbing. We are the ones who didn't reach standard screening age yet. Sometimes we should have been screened earlier than age 50 and didn't know it. In my case I did not know that my grandmother died from colon cancer (I was told probably liver, but not certain). I also did not know that both my mother and father had multiple polpys removed at their first screening colonoscopies. Especially since I had one primary cancer before, I should have started screenings earlier, but I did not know that. My husband had 5 polyps removed at his first screening at age 50. His son knows he has to start at age 40. My children know they have to start at age 35. (One son had his first already at age 19 due to symptoms and family history.)
We need to spread the word everywhere we can, that people need to know their family history - if parents had polyps removed before age 60, they need to start screening earlier. If they had relatives with CRC they need to start screening earlier. But they also need to know that cancer plays by no rules. There is no "magic" age to get any cancer. Everyone has to be an advocate for themselves, and if they have any changes in bowel habits, including blood or mucous in stool, thinning of stool, or if they have unexplained abdominal pain or bloating, fatigue, anemia or weight loss, they need to see their doctor. And they need to keep pushing for answers until they get them.
I don't fit your criteria because I was diagnosed before 2012. But I see others who have replied diagnosed other years anyway. I was dx'd at age 47 in 2009 after being misdiagnosed for 2 years. Stage IV.