The problem with the jobs you're listing is that they are tied to the individual's physical health and capability. A 50 year old guy can sit at a desk and work,

The problem with the jobs you're listing is that they are tied to the individual's physical health and capability. A 50 year old guy can sit at a desk and work, but many 50 year olds don't want to go fixing roofs. Sure they can run a business and hire other plumbers/roofers, but then they are doing desk job again.