My dad was diagnosed with bowel cancer in October that had been initially missed in check-ups following a previous (unrelated) cancer. He died two weeks ago.

His dad, my grandfather, also died of bowel cancer. Both were in their 70s when they were diagnosed and died. There is no knowncondition like FAP or Lynch syndrome in the family. 

I am 46 and hoping for some insight into what additional screening might be available to me either now when I turn 50. My three siblings have all been offered a colonscopy but they are either over 50 or have had a positive FIT test. 

I am not overly anxious about bowel cancer as I know it is mostly not hereditary, and neither my father or grandfather were diagnosed at a young age. However, I have had colorectal symptoms for a long time that so far have been attributable to IBS. My only concern is that any malignant changes in my bowel might not be as noticeable since I already have longstanding bowel problems.

I've read Bowel Cancer UK's information on screening and family history but it's not clear to me whether I would be eligible for a colonoscopy before I turn 55. I have never had a colonoscopy. 

Thank you in advance.