You have made a terrific decision to stop smoking and you should never again smoke cigarettes or joints. You should also avoid occupations that would put you in contact with harmful substances that could further damage your lungs.
Being a carrier of alpha-1 antitrypsin deficiency with a MZ phenotype, you are not entirely risk free. The MZ carrier state increases the risk of chronic obstructive pulmonary disease (COPD), but only with exposure to cigarette smoke and environmental pollutants. Having asthma is an additional risk factor for the development of COPD. That you are able to run 3 to 4 miles a day at a good pace is evidence that you still have good pulmonary reserve. The degree to which lung function improves following smoking cessation is unpredictable but optimum improvement may take several years to become fully manifest and the post bronchodilator lung function should be the measure of improvement. Your lung function may or may not ever approach predicted normal values but you can be assured of significant improvement over time.
The diagnosis of COPD can readily be made in people under age 35 with a ZZ phenotype, especially when predominantly emphysema. The specialist is right to the extent that making that diagnosis in non-Z carriers at an early age is probably inappropriate.
If you should decide to have children, you and your partner should definitely have genetic counseling.