Yes and there's a scientific reason behind that even tho this is just a fiction, his frontal lobe is not fully developed yet, not only that, his physical development is also a big factor as to why he "acts" like a child. Any children who claimed "they have a past life" are still acting like a child in reality, why?? It's because their brain is still underdeveloped, they're still developing, so it makes more sense for them to act like a child, this is why I also associate Nahida from Genshin as a child despite being 500 years old and in God years, she is considered a child because she's still a branch from irminsul (kind of like a world tree) and many people confuses that she's adult or a child but she's still a child because she's still developing or growing

I swear, it’s so easy to forget that he was a 15-16 year old teenager before he transmigrated. It’s so great to see someone who transmigrated acting the age of the person they became.
I’m also so glad that they are holding off on the big bad appearing. I’m guessing it will have something to do with the dark miasma that Franz can see. But when they have the big bad show up while the main character is still a kid, it can get so tedious at times. So I’m glad they’re keeping up with the wholesome fluff for right now.