Hello Stefan,
I hope you're still alive but I wonder how you take care of your health. I know you're a couch potato detesting activities others than quick movements of your fingers over the keyboard so imagine how surprised I was having read you want to lead a healthy lifestyle.
I can tell you I have a five-kilometre run every day. I also bike to school and go to a gym twice a week. It makes me pretty fit and I guess it's enough to be in shape. If you want, you could follow the same path.
However, I believe that it'd be easier for you to start with just walking for about thirty minutes a day and after a few weeks try running. Not too much for the beginner :)
What do you think about it?
Henio