So he had the time to go "to the east" and learn under an ascetic monk in the 5 years in which he left to fight in the war, led a mercenary company, learned to read and write by himself, carpentry, accounting, animal husbandry, cheese making, the particular habits of every magical beast, and a hundred other things. Also, he says "children normally play at 16", but when he was TWO years old he decided without being prompted to leave the house where he was being raised and go live in the forest by himself. Whose standards is he using when saying children should be playing at 16?
Plus, he's been gone 5 years, and we know he met Elizabeth at about the same time that he left, so he earned the "demon mercenary" nickname almost immediately after he left the village (and was throwing an 11 year old girl around as "practice"). So when did he stop being a mercenary to go to the east? And he also says they use the crossbow in the "west", so where exactly is this village, which belongs to neither the east nor the west.