Eh, what's wrong with people in their 30s and 40s, eh? EH!?!?
More to the point, he is not supposed to be the hero from Gothic - no connection between the two worlds.
The nameless hero thing is a design choice - it provides a blank slate, i.e. you can project your own imagination on the hero more easily (in contrast to say the witcher or mass effect or now DA2, that have a rather defined main hero), and secondly it avoids problems with voiced dialogue that would come up if you were allowed to choose your own name your character.