“[M]aester Lewin says bastards grow up faster than other children.”
“That’s true enough,” Benjen said with a downward twist of his mouth.
Yikes! One could charitably assume that they mean “bastards grow up faster *psychologically* because the world is meaner to them” (and I do think Benjen means it in this sense). But coming from the Maester, it sounds rather cruelly pseud0-scientific, along the lines of “mongrel puppies are healthier than purebreds.” If Jon had to grow up hearing this kind of thing, it’s unsurprising that he’s as bitter as this chapter shows him to be – and surprising that he hides it so well and is so magnanimous in his actual behavior (e.g. initially foregoing his claim to a wolf pup, and kindly comforting Arya when, as we learn in her first chapter, she commits the unwitting cruelty of coming to *him* for reassurance that she’s not a bastard too.)
He’s not a perfectly shrewd observer, though: his identification of Myrcella as “insipid” will prove incorrect.