I've climbed off and on over the years but never really practiced or did it regularly. Perhaps one trip to the climbing gym every other year. This past month, I've replaced some of my weekly trips to gym for lifting with trips to the rock climbing gym for bouldering. I'm at that early time in the process of learning something where progress is very quick. I've only taken two one-hour courses and gone about a half a dozen times in the past 3 weeks and am pretty amazed by the progress I've made. Problems (the name for routes in bouldering) that seemed totally impossible to me a week ago even this past Saturday are now easily doable.
One of the things I've learned about bouldering is that if a problem seem too tiring or if it seems like I don't have enough strength, I'm probably doing something wrong. Usually poor technique is to blame. In fact, this is a good indicator for a lot of activities in life...people over estimate the amount of strength they need and underestimate the role of technique as a multiplier for the strength you have.
It's amazing how quickly we humans can learn both mentally and physically. And the sense of accomplishment it gives you from seeing the progress is enough to overcome any mental rut you might find yourself in. Give it a try!