you cannot grow a stronger jaw. what you are admiring in other people is their jaw bone, not their jaw muscle lol.
I know jawbone is the case. I have good jaw, but when I clench my teeth I can feel the muscle pop out more, so why is it not possible to get it even bigger ?
Probably is possible. Why would you want this part of your face bigger?
It looks better to have more defined jaw
Look into "mewing" if you have a tendency to mouth breathe. Other than that your jaw is shaped by your tongue posture and teeth when you grow up.As an adult there wont be significant changes unless you get surgery.