A friend of mine climbs. In fact he's doing Nanga Parbat this spring. He's made the top of 12 of the 14 highest mountains in the world, and has done 5 climbs of Mt. Everest, without oxygen. His name is Ed Viesturs. I believe he's recognized as America's premiere climber now.
You must really be in good physical condition if you are climbing. It has to be one of the most demanding challenges there is.
I told Ed I'd join him on top of Mt. Everest as soon as they put in a cable car that takes me to the top... it's the only way I would ever get above a base camp.