For the person who's doctor told them not to ride I say find another doctor. As perfectly illustrated in the above posts exercise is ALWAYS a good thing! I can echo what the others have said. I've lost weight (40 lbs since last February). I feel vastly better! My mood swings have toned down. My outlook on life is better! If riding a bike at 51 is somehow a bad thing I say pooey on you! Some of my friends have done exactly that. They think my wife and I are nuts. It's interesting that the one's who make the most negative noise are the typically the one's who don't exercise at all. And it shows...
My wife and I will continue to ride until our bodies refuse to allow us to. If cycling is like crack then I am happily addicted!
So if you are reading these posts and wondering how to get back in shape do what the poster above said - Go buy a bike!!