Genetics plays a large part in anyone's physique. I'm not talking about being fat because people in your family are fat, I'm talking about how much muscle mass a person can build naturally. I come from a line of tall thin Germans and short stocky Italians. My lean body mass is 182lbs. At this point in my life (52), that number might fluctuate +/- 5lbs depending on the time of year and how heavy I'm lifting. I've been blessed with strong, muscular legs and don't have to work them that hard - which is good because I can't do squats anymore.
I don't worry about numbers because I don't take numbers to the beach. I look at the mirror and get all of the feedback that I need.
Eat healthy, lift heavy, do cardio, mostly - have discipline. That is the magic formula.