Do you mean you smoked for 20 years, or that you lost 20 years of lifespan due to smoking?
If it's the latter, I remember reading in a medical study that the adverse health effects of smoking are mostly reversed several years after the person stops smoking. :)
I used to be a reasonably heavy drinker, then I quit more or less cold turkey, didn't drink a drop for over 6 months, and even though I've now gone back to drinking a bit, I'm very careful now to limit my intake to well within the health guidelines (i.e. no more than one or two a night, no more than a couple of nights a week). Not only has this done good things for my health, it's done great things for my finances.
Other damage is certainly done to the lungs that can cause other issues--emphysema, cardiovascular problems, etc--but the risk from the "scariest" threat out there is greatly diminished.