I have often had the same thought. My great great grandfather joined(by force) the confederate army at the age of 40 years old and fought in the infantry, marching everywhere he went.
I have often thought that when I was 40 years old, there was no way I could go fight as an infantryman.
The Civil war was brutal because of the rifle and repeater arms. The wars fought before that was hand on hand fighting and that had to be hard to do as compared to how we fight today.