My dad has been smoking for over 30 years now. If he quits now, would it make a difference? His lung is already damaged, right?
There is damage that has occurred and also ongoing damage that happens every time he lights up another cigarette or someone else does around him! there is great benefit both immediate as well as long term if he quits smoking! it does not matter how long he has smoked.
He will enjoy better health immediately and immediate risk reduction for lung cancer as well as cardiovascular disease.