To no degree
http://www.ucalgary.ca/gazette/april7-03/hepple.html
Isn't it true witch after age of 21, people shouldn't grow new mucsle cells. You can flatly expand muscle tissue you allready have thru weighttraining but muscle cells lost--due to fasting, prologned inactivity, aging--are gone for good.
added to pre-existin ones in people past the age of 21 simply by exercising.