As always, the MC's knowledge and perspective is all over the place. Like the MC thinks his childhood play was normal, but calls Elizabeth and Fen geniuses for being able to do a fraction of what he could do at their ages. He also thinks his play was normal, but worries all the time about the children in the village and built a playground for them even though he left to live in the forest by himself at a younger age. So the author wants him to know what is normal development for others, but still think his childhood was "normal".
Another inconsistency is, how does he know so much about magical beasts? If we go by his years living in the wilderness, he should have knowledge that matches his experience, but not be aware of the names that the people of the kingdom use for the beasts. For example, he corrects Elizabeth that it is not a "great snake" but a "great iron snake". To be able to make that distinction, he would have had to learn in the kingdom about the monster species and their names. But he should have been spending that time fighting humans as a mercenary, not learning the behavioral details of rare monster variants that live away from people.
The author wants the MC to know everything and be competent at all skills, but also be someone with no formal education and who was isolated from society until five years ago. Apparently mercenaries in this world have access to accelerated courses on everything, even though most people are illiterate.