Is very common and normal that there isn't a large amount of fat around your ribs so no worries . now lets move to the arms , seeing your profile identify you as a male i would just directly assume that you are just lacking muscle mass, as a 14 male your metabolism is running in extremely intensity , try doing some basic work out such a push up and plank daily , belly is where most fat are store so is the last part of your body to lose all the remaining fat.