He's probably in his 20's now since her younger sister is already in college. But when he entered the facility he was wearing a middle school uniform so maybe ne was 14-16 back then
*his younger sister
Its complicated.┗( T﹏T )┛Short answer: 12-15
Long answer: Technically in his 20's, but physically he hasn't grown at all, and his mental age is really difficult to guess due to his world view and difficulty expressing himself. Toshio is naive, childish and innocent, and smart, responsible and independent (on his own way ^^) at the same time.
So, Toshio is Toshio. (⌒▽⌒)
I was like oh i wonder if they sister will come up again and SHE DID !!!
this is a very sad story for such a cute character I do wanna know what age he is obviously super super young and a child