I seem to average 10 hours per week on activity (cardio and strength) in the warmer half of the year and 8 hours in the colder half and that is pretty satisfying and keeps me healthy.
20 hours/week would seem like a lot to me. After 90 minutes of riding, 45 minutes of running, 60 minutes of walking or 30 minutes of weights, I’m happy to be done.
I’m still doing what I do in the work world and don’t really want to quit outright but will probably want to transition to less than I do now in a few years when I’m close to 65.
Otto