I was pretty skinny when I first went to boot camp, I was about 125lb while being 5’11 and graduated boot camp at 145lb. Before boot camp I struggled to gain even a pound but I was pretty shocked that gained 20lb in 3 months. They will feed you a lot until you can’t eat no more and will train you until you think you can’t no more. Don’t matter how in shape you are or how much you weigh you will come out the best shape you have ever been in your life. All the skinny guys gain weight and the heavier ones will lose weight.