I'm certainly not an expert at it but I've been getting ready for elk hunts over the years and will tell you what has worked for me. Main thing is that your upper body won't carry you over the mountain. The legs would be the main focus. I try to maximize my training by finding steep hills and walking or running them. The steeper the better and add weight in a pack as the weeks go on. Don't overdo it when it comes to training or the weights. At your age you probably don't have to worry but as you get older the muscles and joints don't work as well and I for one have hurt myself by pushing it too hard too early. I now try to make it a year long thing. You'll get alot more positive alot quicker by running hills then flat ground. In the weight room, work on lunges, pullups, abs, dips, etc. plus if you run the treadmill work on bumping up the incline a little each week until you are doing 10 to 15%. Is it fun running/walking hills?? Maybe not so much but the work you put in now will pay when you get there...