Responses
His exact age is never mentioned, but I think he's likely 19, give or take a year. Shima says he can start college right away which means he's at least 18. Shima also calls him a child though, and the age of majority in Japan is 20, so by that definition he's 19 at the oldest. If he calls him a child simply because of their large age gap, then it's possible he's above 19, but based on his behavior and appearance he can't be much older than that.
Thank you!
I know Yakumo is young, but exactly how old is he? I don't think that I am remembering that I ever saw a reference to his actual age other than young or college age. If anyone has this answer, thank you from the bottom of my little Yakumo adoring heart.