So at nine years old, real world seonwoo got pulled into the game world and for now we have to assume there was a game world seonwoo who shifted to the real world. They each lived there for 20 years. Then as a 29 year old adult, when game world seonwoo played and finished the game in the real world, he got pulled back into the game world and this is where the story starts. At the same time, real world seonwoo who's been stuck in the game world for the past 20 years went back to the real world. Right now we are seeing his life after he came back. That is the same timeline as the start of this story.
The mom did mention that seonwoo was saying something about wanting to become a hunter to kill monsters and laughing about it, we have to assume 9 year old game world seonwoo said this before he realized this world did not have those things. Which means game world seonwoo also might have had a real childhood inside the game before he came to the real world.
Although why he alone cannot remember his childhood is still a mystery.

What just happened?? Or am I the dumb one not to get anything??