i walk 5 miles 4-7 days a week and if everyone did just that and nothing else it would eliminate a great majority of health issues. I am 37 and plan to do this until I no longer can. Walking is the perfect exercise in that you can easily multitask with a podcast, phone call, listening to music, writing/dictating. It is very low impact so the likelihood of injury is pretty low. You can do it anywhere on earth and need only a good pair of shoes.