This concept behind earlier screening is a whole thing amongst medical professionals, and a point of controversy in a number of specialties.
As with most things, procedures have risks and benefits. Colonoscopies have risks too, right? Bowel perforation (bad news), bleeding, infection, etc. So, balancing that with the obvious benefit of catching cancers early, the USPSTF (United States Preventive Services Taskforce) made some recommendations on when patients should undergo screening for colon cancer.
As of right now, per their highest level of evidence recommendations, you should get a colonoscopy starting age 50, and every 10 years thereafter. Note, I said colonoscopy. Not sigmoidoscopy, not stool testing, etc. Those have different guidelines and intervals (but do still start age 50).
If you have family history of colon cancer, or certain diseases that put you at higher risk for colon cancer, the recommendations are significantly earlier. In the case of a positive family history, you get a colonoscopy age 40 or 10 years before the earliest colon cancer diagnosis in the family, whichever comes first.
The reason I bring all this up is to point out that if you go to the USPSTF web site, you'll see an evidence level B recommendation to start screening age 45 as well. You'll also find the American Cancer Society has colonoscopies starting age 45.
The evidence and safety for colonoscopies at earlier and earlier ages is getting better and better. Doctors should absolutely be screening well before age 60. If your doctor isn't following uspstf guidelines due to practicing outdated medicine (some variation due to personal preference/evidence based practice I guess is acceptable), in my not so professional opinion you should probably find a new doctor.