Most of the blame for the progressive age related decrease in exercise capacity is correctly directed at the cardiovascular system. Traditionally focus has been on the maximal oxygen uptake ( O2 Max) decrease with exercise with both components of that value , the cardiac output and the a-v 02 difference both contributing.The stylized physiological narrative is that O2Max decreases about 5-10% per decade on average although there are some outliers whose per decade loss is much less. It has been suggested that about half of that loss is due to decrease in the heart's stroke volume and about half of the blame goes the a decreased A-V o2 difference-i.e. the ability of muscles to take up O2 efficiently.The benefit of exercise in heart failure is likely due mainly to the effects of exercise on the muscles and their mitochondria and capillary density and less on making the heart beat better.
O'Donnell and co-authors in their paper "Physiological Impairment in Mild COPD" tell us that mild COPD and the effects of aging are qualitatively similar While arterial blood gas values change little and acid base balance is maintained there are well described age related functional and structural changes.
Airway resistance increases as large and small airway narrow and there are also some age related enlargement of the air spaces.Residual volume increases while inspiratory capacity decreases while total lung volume changes little.Airway resistance increases as air flow increases and compliance fall a phenomenon called frequency dependent compliance, once a source of interest to pulmonary physiologists but not so much with pulmonary doctors.
When older endurance athletes are compared with young subjects several workers have demonstrated that the older subject have a higher ventilation for a given work load.The minute ventilation (VE and VE/VCo2) are increased said to be due to greater dead space ventilation which is considered one form of ventilation perfusion inequality. The mechanism for this V/Q imbalance is not clear.
So getting older, lung wise is a bit like mild COPD similar to getting older heart wise is similar to a little of diastolic dysfunction.-more on that later.
O'Donnell, DE et al. " Physiological Impairment in Mild COPD), Respirology , 2015 doi 10 1111/resp.12619 Published on line 2 Sept 2015