Well, what do make impossible growing after some age? The bones growth plates. Some grew until 23years, some until 18.. But it is all about the bones growth plates. If you are thin and you star to eat well and go to the gym, after a while, your muscles will be bigger. If you dou steroids, your muscles will be so much bigger. Your skin, nerves and muscles have the capacity to grow and shrink. The human body is amazing.

So it is supposed that your muscles can grow as well with Limb lengthening. Maybe no as fast as you lenghten your bones, but they can grow