For a decent number of guys at (and an even larger percentage under that age wise)18-22 and even a little older if you have an real amount of physical activity, even with unlimited food they simply can't put on weight. I was one of them and was eating 6,000+ kilocalories a day. Almost 3x what the recommended for adult guys is. Most of the guys with metabolism like that age 26 and under are plenty strong, might get moved around due to not having a heavy enough base leverage just losses out, just not worried about weight on guys under 24, unless it's fat and out of shape.