I know that, genetically, a person can be better or worse at gaining muscle. It's not a massive improvement or detriment but it can make the difference for cutting edge bodybuilders. That extra couple of percent muscle really makes a difference when you're competing with the best of the best. But as far as normal life goes... it wouldn't make that much difference, when weight is concerned the genetics regarding height will be the primary decider. The tall person will still have to eat more than the short person to weigh much more though, if they ate exactly the same amount you'd just have a taller/skinnier person roughly the same weight as the shorter person. Physical activity makes difference too. Muscle takes a lot more calories to maintain than fat, so if you're very muscular, you'll be lighter than someone who is very fat when you both have the same calorie intake. (Not only the calories needed to stop the muscle breaking down, but the calories needed to stay active enough to keep the muscles built.)