like others said - it's a good idea to practice hiking with weight. I'd make one small modification though - make those practice hikes weighted with water in the pack. Get one of those 2.5 gallon water jugs and empty it halfway. Once you can handle that weight, fill it up all the way. Once you can handle that weight, grab an extra gallon. The benefit to using water is if you find halfway that you're just pushing yourself too hard, you can dump some of the water real easy. And for reference, water is 8 lbs per gallon. This makes the 2.5 gallon container a 20 pound weight, add the weight of the pack, and you have what is likely going to be your trailhead weight.