Iggy.. this is how I started too! Our family got a puppy, and boy.. this puppy had so much energy. So, I started walking her to burn off some of that energy.
But I was appalled at how winded I was getting in such a short distance. so I started walking her everyday, and I noticed that I could go further and further without having to catch my breath. and I would feel good afterwords. Kind of energized and relaxed at the same time. a good feeling.
and.. my puppy would be pooped (literally and figuratively :P )
My dog just turned 9, and the vets keep thinking she is about half her age. I think it is the exercise (she also loves chasing a tennis ball my son throws for her all the time). She had to have surgery, and the vet said her recovery was very fast. He said that part of the reason was her excellent muscle tone. and I have heard this about people as well. The better shape you are in, the quicker you recover from surgery.
so.. there are many benefits from exercise. You don't have to be an athelete. hey.. all you need is a dog!!!
(but don't use not having a dog as an excuse!).