"I am still, at 70, a candidate for lung cancer."

This is true, but your risk has been cut at least in half!

That said, lung cancer is not, nor has it ever been, then greatest health risk with smoking. Of the major medical issues that smoking can cause, the most likely one is cardiovascular disease. Quitting smoking can reduce this risk almost to pre-smoking levels. Lung cancer and emphysema approximately tie for the #2 spot at a bit less than 10% each for people who smoke 1-3 packs per day (and, from what I hear from sufferers and doctors, you'd probably prefer the cancer to the emphysema.)