People asking where people are getting the "40 yr old Link" impression from need to actually look at his face, not the youthful hair and hairstyle around it.
Sans hair (baldy) or with short hair only, that is a face befitting a man in his forties.
The hilarious ever-so-slightly bulbous nose and cherry shaped chin, as well as the slightly furrowed brow, are facial traits of an older man and make for a bizare juxtaposition with the youthful hair, teenager's body (slimness) and clothes.