Two things you can likely count on, 1) hiking a lot, and 2) carrying a backpack, hopefully full of elk quarters. That being said, you need to focus on several things.
1) As mentioned above, you need to increase your exercise capacity/stamina. You aren't running a race so start early and slow and work your way up. Going further and longer each day. I am in my mid to late 30s and prefer a mix b/w an exercise bike and waking on a treadmill at an incline.
2) Strengthen your core (shoulders, back, abs, & thighs). There are many exercises that you can do at home w/o weights to do so. Or if you have acces to weights that is great to. Some examples are "planks", lunges, squats/wall sits, calf raises, etc.
Backpacker magazine or backpacker.com has some great exercises and workouts that will get you in shape for sure. If you have trouble finding them pm me and I can email them to you.
3) last but not least is stretching. Even while on the hunt, stretch before you hike as well as after. It will save you from injuries. Good to start now before and after exercising. I will confess, I don't always practice what I preach