If your goal is to keep yourself healthy and fit, you can really focus on the quality of training rather than quantity. Choose something that has the highest benefit-density and you can bear with, and then just do that. Climbing and walking your dog can already keep you fit. Stick to them . Do other activities just for fun, no need to push yourself too hard. :-)

And you think climbing is easy? Maybe for beginners. But you will definitely need some other trainings to enable advanced climbing. This activity alone will keep you busy for very long.