
That won't help and ruin the story's foundation. He is a child in the past and the MC treats him as such but years have passed and he's grown. And more than anything we have to remember he's a dragon, a being that existed before even taking any form whatsoever. What he lacked was knowledge. If he was really a child then that would've been weird tho.

I'm not saying he's mature but that he's a spiritual creature. Among his folks he'll be considered a child even after a 1000 years in front of an even older heavenly being. Which is why he cannot be compared to human children. His age cannot defy his knowledge. He can be whatever he wants to be. Just like Ryeo-ah, she looks like a child, talks like a child and even sometimes acts like a child. But she's more than 100 years old and is knowledgeable.
Ah it still feel so weird to me that the mc call ml 'apple of his eye' and a 'child' and then they are going to be sexually attracted to each other??? Yeah, sure he is a dragon but he act like a kid.
I'm okay with their present relationship..just not the past, the found family duo turn to lover dynamic that the author is doing right now. I hope mc will refuse and died somehow, and then it will bring us to the present. But this time its different for mc because despite knowing all of this, he cannot relate to it and see ml as his son as he is a different person now.
Sadly from the spoiler in the comments this will not be the case. Maybe I will drop this or skip this part of the story.