Is bypass surgery with three blockages fine at the age of 75. the patient also has high diabetes for many years and takes insulin?

Yes. It is best to follow your cardiologist/ cardiac surgeon's advice between the choice of angioplasty vs bypass with pros and cons.Good luck

If the blockages are severe involving important arteries and are bypassable, it can be performed if your cardiologist feels that it is necessary for control of symptoms or preservation of healthy heart muscle. Diabetes increases the risk especially diabetes has also affected kidney function. His doctor is his best guide as to how to proceed. I wish him good luck.