You see, it is totally an individual matter of the condition of the patient at age 75. Most people are retired, but not disabled. Bypass surgery
is no longer experimental. There is a good prognosis for most patients, even at the age of 75. There is a quality-of-life issue of whether other medical techniques may be more or less effective (stents, versus medicine). There is the overall physical condition of the patient, and other possible complications. (Unfortunately, cost factors as well.)
But, since modern medicine has developed bypass techniques, the chances for a good quality of life long after 75 are now able to be achieved.