Apologies, skimmed through the thread. If you are in England then you may get invited to have a sigmoidoscopy when you are 55. Otherwise the bowel screening programme will start when you are 60.
As a disclaimer, I'm not a clinician, but have done a lot of research studies in the cancer area.
Most cancers, 60% of bowel cancers in fact, are diagnosed in people over the age of 70 years. Primarily cancer is a disease that affects older people. That is the reasoning behind the screening starting at 60. However, a family history of of the disease, of polyps etc is different.
At present, the test that is offered at 60 is not very good and the screening programme is in the middle of changing to a better one.
Few cancers are actually picked up by screening. People still need to be aware of the symptoms that doctors class as "red flags". Change in bowel habit, rectal bleeding...the Cancer Research UK site has a lot of information and i would suggest that anyone who is worried checks it out.
If you have a family history of bowel cancer, ie a first degree relative had it, then you may be at a higher risk and so wel, worth talking to your GP