Your conditioning will come in time. But if you want to ride to get back in shape - you gotta ride. is it possible that you could take your bike when driving your son to his activities. Even if you can ride a mile or two - they do add up. You are not alone - life is plain tough. Let me know how your riding is going. I am a little guy 6' 2 and a modest 257 pounds according to my last weight-in at weight watchers.
Chris