.....I have found that just doing one set until failure or almost failure, of bodyweight exercises works best for me. This way I can exercise daily without risk of wearing out my central nervous system, which has happened in the past when I did very high volume calisthenics. So as for me, as I have gotten older, I have gotten a little wiser, thanks to my body talking to me! I have also found that by doing just one set of my exercises, I can then do my walking for cardio, and not feel totally wiped out aftewards, leaving a little "gas in the tank" for other important activities. So, in a real sense, undertraining so to speak, works better than overtraining.