Hardly conclusive evidence for anything, but an interesting observation from the Maciejowski Bible.
Boys and very young men are shown with short, curly hair -- i.e. young David slaying Goliath, Cain and Abel as children.
Older, but still young men are shown with that jaw-length, curly with the short curled bangs style that you see everywhere. Some are clean shaven, some have short beards -- David after he becomes king, older Cain and Abel, random dudes in general.
Older (or more distinguished?) men have long, wavy hair, parted in the middle, and thicker, fuller beards -- Noah, Jacob, and...um...God.
Beggars and vagabonds also seem to have the same general styles according to age, though their hair is often more unkempt.
It might just be more of an artistic device than an actual practice, but I thought it was kind of interesting.