Considering our mc's mental age is over 30 years, he sure says pretty stupid shit sometimes. The kind of things you wouldn't expect an adult to say to other people regardless of their age (like how he commented his sister not being feminine).
Shit like that is just uncalled-for.
I (pretty much) always get the idea that these authors have their "adult mind in child's body" -mc's behave how it suits the situation/plot the best at that moment.
There's hardly ever consistency with how they act and think regarding their supposed mental age.