If you do not live in Arizona, you might not realize how cold it can get here at times. In the desert areas you can go from hot to freezing in a 24 hour period. Those clear nights can get really cold. I work in that all the time. I teach a nature course where i take students out into the desert for camping and learning about the natural environment. Then I go and see a chiropractor in Phoenix every time I get back. The work was hard when I started this, and it is a little harder now.
The issue is not me getting older as much as it is that kids are used to having stuff done for them. Most of them come into this thinking it is inherently safe. Even though we have a full disclosure and waiver for parents to sign, there is that mindset that this is like a fancy theme park event. They think it is made to be scary at times, but that nothing bad can happen to them. Then, all of a sudden, something will happen and open their eyes. One know-it-all kid slipped on a rapel down a small cliff on the last trip. I did a job on my back keeping him from banging himself up even more against the rock face. He was in no danger of falling as his line was belayed from below.
On other trips I might get worn out gathering the raw materials so the really unprepared kids do not get hypothermic on a cold night. Even a small fire is tough depending on where you are at in the desert. It is non-stop moving, instructing, checking and keeping the kids out of trouble. My head is on a swivel along with my assistants keeping kids safe from snakes, scorpions and more. My back really gets sore now sleeping on a thin camping pad under the stars. I would never want to give it up though. I just see my chiropractor in Phoenix when I get back. I get some therapy and adjustments for a few days, then I go back out ready to tackle another tough group of pampered kids.