The best climbers need it all - power, balance, agility, focus, endurance, natural physical ability AND brains- a apptitude to figure out the route like working a puzzle. Also guts (that is where I was not up to par.) Strength however is not brute strength, but strength per weight. You have to have the strength to get your body up the rock, never mind that 220 pound neanderthal climbing next to you. Lyn Hill is a tiny woman and at one time was about the best climber in the world. SO, the ability to keep climbing as you get old requires you to keep your body weight down. The loss of strength with age is bad enough, but add dead weight to that, and it is all over.