My golden retriever, he is approximately 13 years old, is in alright shape. He is not overweight. He is average stature. But for some reason he breaths heavily often. Even when not doing physical activity he will breath heavily. As in he could be just walking about the house & then all of a sudden he will start breathing heavily. He does not get much physical activity because his legs are not strong anymore. He has a hard time getting around & whenever I take him on a walk he only lasts a couple blocks then gets extremely tired. Why does he breath so heavily? Lack of exercise?