Responses
No one really knows as it is yet to be verified by the author but a lot of people have speculated he is within the age range of 16-18.(▰˘◡˘▰) As for his adult form in the game as the final boss he appears to be within the age range of 22-24.
does anyone remember how old the demon king is? the isekaied guy too for that matter. it just popped into my head and now i'm really curious.