My experience is something like Butch reports. At 45 I was better than I had ever been or would be, as a climber. At 50 I was still stronger and more productive than nearly any climber I crossed paths with. But somewhere there in the next 5 or 6 years, breakdowns in capability became obvious to me...though I still had plenty of tree people saying I hadn't lost a step, and not many much younger climbers kept up. But trouble with both shoulders and elbows, some back pain on occasion, many a little niggling thing crept in.
The real killer was the hip joint failure. At 50 it was just beginning to hurt on occasion. Within just a couple of years it was a constant issue, completely compromising my movement, both aloft and on the ground. It murdered my work, my recreation, my love life, my self esteem.
I finally had that mofo cut out and replaced with titanium, cobalt chrome, and cross-linked polyethylene at 58, and a year later, maybe 18 months, I was a new man. Five years on, still amazed at the change in quality of life this seemingly simple thing has wrought.
So sometimes you can turn the clock back, with the right medical intervention.