Well, I am 50 now and I can't imagine that either. I have a cousin who is, let me say politely, a blowhard. Just recently he was saying how he would have liked to have been part of the war, getting to sleep out every night and "live off the land". I told him if he wanted to try it just take his shotgun and hit the woods for the next 4 years or so, and be generous to yourself and dress warm and wear a good pair of boots. Leave your aspirin and cold medicine at home and don't even consider bringing roll-aids or pepto-bismol.
Can you imagine something as simple as taking "rest breaks" while on a march. I do good to drive to Baton Rouge (2 hour drive) without stopping in at a service station etc. I don't believe folks ever stop and consider just what these men endured. I think of Hood's retreat from Nashville and shiver at the thought of being there. Doing it at age 50 is beyond my comprehension.