BlackDog:
I told this to a smoker and it freaked her out so much she tried quitting; so I'll tell you.
Cigarette smoke contains known carcinogens. Carcinogens are substances that MUTATE your DNA.
If you get a mutation in, for example, a gene that helps regulate cellular reproduction, and the cell starts reproducing indefinitely, you have cancer.
Inside your airways sticky mucous is secreted that absorbs foreign particles. There are little hair like growths that are driven by motor proteins that help move the mucous up your airways. Nicotine causes these hair like growths to stop functioning so that your airways can no longer function normally in removing any foreign substances.
Just because there are old smokers doesn't mean that even these survivors have not suffered serious consequences to their health through smoking. Most smokers do suffer, chances are you'll be one of them if you continue. However, there are genetic factors involved, and lifestyle factors such as exercise, nutrition, etc.
At the end of the day you should need no other reason to quit than it is haram and Allah will punish you if you do not desist