Activity and type of activity plays a huge role in weight. In the course of my rehab as my activity level increased my weight decreased, just as one would expect. Now, my weight is increasing again. Why? Because I am doing a lot of weight lifting and body building exercises. Concurrent with that I have increased my protein consumption but not my calories. So, I am piling on muscle. Well, maybe not piling on, but increasing muscle. The weight gain will continue until I am back to normal for me performance, or at least as far as nerve damage will allow.
Body type and age play roles in weight as well. Some folks have bigger bones, some smaller. Some are short legged and long torso, so long and lean. As we age hormone balance changes with an effect on the body.
All of this reinforces the foundation concept that it is fitness and not weight that is the goal. Weight is a valuable metric to keep the mind straight. But, ultimately being able to perform is what counts.