Responses
According to back story, which is 9yrs ago from the present, it seems he's at between 25-27 (same age as Mina cuz they were batchmates) since he looked like a teenager.
Aaaaand I was right, cuz I went back to Kaiju No. 8 wiki and they already put an age, he's 27.
yeah, i've always assumed he's between the ages of 25-27. thank god he's not younger.
i still wonder how old narumi is...