Quote - If I had to wear one of the wigs that was fashionable at the time, I'd want a nice short haircut (but it's more likely that they've assumed he was subject to male pattern baldness given his apparent age in the painting).

Unless there's some way of determining whether or not he suffered from typical male pattern baldness from the skull, or maybe even from DNA, it's likely they just guessed, based on average statistics.
Maybe they have a foolproof way of determining that - I don't know.
I, however, am a 43 (just about 43 ) year-old male with no signs of baldness or even receding hairline. In fact, my hair is more than halfway down my back, and pretty much all over the place, front and back... at times I WISH it would recede, since I feel bad cutting it. ;-)
My point is, age only implies what's likely, not necessarily what's true.