I started walking three years ago at the age of 55 for ~2000 km per year since. There was Hypertension and a suspected heart problem at this time, so I was cautious about running. I also have a nice area of wood very close to my home.

It turned out quite well. I am officially heart-healthy today, blood pressure went down about 20-25 mm Hg, weight 10-15kg.

Regarding running - I do it the same way I do something for my upper body. Sometimes the body is longing for it, and than I do it. In the case of running: Long walks often give a certain stiffness, especially in the legs. When this happens, I simply include a few (1-3) kilometers during the walk.

I also learned, that it is far easier to sustain such a regime instead the more common forms of exercise. I think its more natural for all but a few people in the long run. Someone wrote here about running as hunting/fleeing which by origin is necessarily associated with stress. I think there is much truth in this.

The only part that becomes sometimes difficult, is the time demand. Doing the math: My 180 km / month are 12km (two hours) every other day. I had to aquire some additional discipline to make it happen.