I too could not eat enough to budge past rail-skinny as a kid. I wish I had that problem now, topping the scale at close to the breaking point.
I think that I wrecked my metabolsim by just not eating much. I hated my mother’s cooking, then when I was in seventh grade my Dad had a serious heart attack and my mother had to go back to work. I had to do all the cooking and i ate even less. I can’t believe anyone ate what I cooked. We ate the junk food though.
I only weighed about 40 pounds in first grade and I weighed 95 pounds when I graduated from high school. Not skinny anymore, though.