At what age do most cases of emphysema begin at? Also, if you have smoked for 20 years and then quit, can the?

lungs rebuild themselves? Do they begin a healing process on their own? I've heard that lung function increases after years without smoking, is that true? When do most people get emphysema? (what age). Answers from doctors are especially appreciated. Thank youAt what age do most cases of emphysema begin at? Also, if you have smoked for 20 years and then quit, can the?
The latest studies show that emphysema can begin developing even in young smokers. Then it worsens with time. Lung function does improve if you stop smoking and further damage is reduced. However, the damage that causes emphysema is permanent. What's worse, the emphysema can continue to worsen even after smoking has stopped.