Japanese grades are defined by birth date, with the cutoff being April 1, so if you’re born on March 31 you will be always the youngest in your grade, while on April 1 you will always be the oldest. So given they’re in the second year of high school (upper secondary school, grade 11), everyone was 16 on April 1st (except for the poor soul whose birthdate is a joke), and their 17th birthday is during that school year.
Incidentally, Ichikawa (
Dangers in my Heart) was born March 31, and the story is set during their 8th and 9th grade (so far), so he might still get a growth spurt… he hopes
![Wink ;) ;)](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)