He said to take up a sport that you love. Rock climbing is my passion as well but most certainly not for everyone. I am in much better shape now that I am a rock climber than before because of two reasons I do it a lot, and any outside trip is a hike with heavy gear. I honestly cannot stop thinking about my next climb and that is the kind of thing that will bring you fitness as a side effect.

If you love (insert sport/fit activity that you cannot stop thinking about) then do that and be super fit because you love it. That was the op's point.