[Sparda4]

Remove 5 years from Issei's current age. Details in the spoiler tag.

Spoiler for Semi large spoiler about Kunou:

Kunou joins in volume 22 the Kuoh middle school as a first year. Issei was 17 in his second year of the high school section. So Kunou is 13 now since Issei is 18 from vol 22