But since you mentioned it. Yes it is absurd as anything in ST because it is Impossible that a guy of shatners age and physical could free climb el cap that far. Saying he was doing a little recreational rock climbing is like saying the Tour de France is a little light bicycle ride.
Impossible. Really. Your proposition is that it is impossible that James T Kirk, who at the time of The Final Frontier would be around fifty years of age, could be able to free-climb El Capitan.
I do not know where to find rosters of known free-climbers, but I was able to find that Tommy Caldwell (along with one Kevin Jorgeson) free-climbed this very mountain last month; Caldwell is 36 years old. Do you wish to assert that it is absolutely, completely, ridiculously impossible to suppose that the maximum age at which this feat can be done will not rise by fourteen years over the coming three centuries of improvements in health, fitness, and climbing technique and practice?
Before you answer, I do wish to point out that the oldest age of any person to have successfully climbed Mount Everest rose from 60 years old in 1993 to 80 years by 2013. (Not the same person.) And that physically demanding task has now been done by a person --- Yuichiro Miura --- whose age is pretty near the expected lifespan for people from Japan; Kirk would be slightly below middle-aged.