My father was 93 when diagnosed with bladder cancer. He declined chemo and radiation therapy and lived his last six months relatively comfortably. My sister was diagnosed with lung cancer in her early sixties and underwent the whole gamut of treatment and while it was very difficult - to understate - she is still alive and well and thriving. It is a quality of life decision.
A work mentor of mine was in his early 70's when he was diagnosed with stage 4 bladder cancer. His doctor missed it when he complained about something being wrong at a previous checkup. Fortunately, the cancer hadn't spread to other organs. Surgeons removed the bladder and he had several rounds of chemo. He looked terrible but managed to drag himself into the office on occasion during treatments. He fully recovered and then dropped dead of a burst aorta a few years later. The aorta problem ran in the family.