>you can't just make someone a laborer that hasn't done that their whole life

You can, my brother and I worked on my Uncle's farm over the summmers for at least ages 14-18 and had no special "laborer" training, we went from high school classes to slopping hog, feeding cows, stacking hay, etc. Sore muscles and blisters are the norm for the first few weeks, but it doesn't take long for muscles to adapt and callouses to form.

Go to gym during the week and do gardening/landscaping work on weekends. Should get you a good portion of the way there.