straight up GS alone time

It hits even harder when you take into account that he's a young man around 20 y/o.

Totally. We can only feel for him.

I think that in these stories he's even younger than 20(?)

They become adults at 15, and he kinda just become an adventurer. Let's say more or less one year now.
And he's been training for something like 5 years, and in the his village he was around 10.....

So I would presume he's still around 16 y/o (?)

possibly, and that makes it even sadder