Since I've never packed an animal like that, I'll have to show my ignorance and ask a stupid question: Are you packing the whole thing, or do you take multiple trips? I'm not in great shape, I could pack out one of our tiny whitetails like that, but I'm going to guess a Mule deer is quite a bit biggger.
In the spirit of the thread, I am 37, 6' 200lbs, I have been easy on my body so I feel good. We live at about 3000' feet elevation and I can walk for miles and miles without being tired, many times with a kid on my shoulders. My phone says I average 4 miles a day and 20 flights of stairs a day at work, so walking is a normal activity for me. Want me to run? Now that's a different story. Get me in any kind of elevation and I'll be sucking wind and feeling sick for a couple days. I'm not exactly healthy, but I'm working on that because I want to do some hunting that doesn't involve sitting in a blind for hours at a time.