Technically, he is not. Remember he was a king who won many wars and was fear by ppl. He is the body of a child but he still got the mind of a man who went through a lot and the skills plus the magic n stuff he gets from his second life.
Still a child even tho he has a mind of an adult his childish ways show when he's being treated like one are with other children.(⌒▽⌒)
That's the joke ma'am
Oh I also think the only thing he knew from his life before was how to use a sword and that's what he has the most trouble with and others see that his skills don't match his size and it looks clumsy.
Woah this child is too badass