If your other was diagnosed at age 53, then you should begin having colonoscopy screening by age 43. Be vigilant, early detection means a lot with colon cancer.
I don't think it is hereditary because they got their colon cancer at the age wherein a person is at risk of colon cancer. If you have this cases in your family, it is a nice move to have a test for colon cancer at your early age.
Best Resource for Colon Health Information
Colon cancer can be extremely hereditary! My mother-in-law has 4th stage colon cancer and it was recommended to my husband and his sister to have a colonoscopy at 40 years old. He did and they found 1 small (3mm) sized tumor that was found to be pre-cancerous. His sister's result was clear. So, that's 50% chance right there. I agree with quinroxanne, be very vigilant! Good luck.
I am well aware of the hereditary nature of colon cancer, I am the 4th generation in my family to be diagnosed with it. My father, grandmother and great-grandfather all died from colon cancer. I think you mixed us up, I said be vigilant and it was quinroxanne who said she did not think it was hereditary!