Can very early age of smoking cause endstage emphysema or can it be reversed?

Yes. The more you smoke, the more damage to the lungs. Smoking early and often gets you to end stage lung disease faster. Quit smoking as soon as possible. Emphysema is not reversible and does not have effective treatment. In some cases lung transplant is an option.
Yes. Emphysema cannot be reversed. The longer someone smokes in their life and the more cigarettes they smoke, the more likely they will develop emphysema and the earlier they will develop it. That is why every smoker should quit smoking as soon as possible.
Depends... The risk of developing COPD depends on the amount of cigarettes smoked over time. The more you smoke and the longer you do it, the higher your risk of developing the disease. So, the earlier you start, the more cigarettes you will smoke and the higher your risk will be. Once present, it is not reversible completely although some improvement may occur over time.
Depends. Not everyone is susceptible to smoking. About 25% of people who smoke the equivalent of one pack per day for more than 15 years develops COPD which includes both emphysema and chronic bronchitis. Once emphysema develops there is no cure and no way to reverse it.