Middle School is years 7-8-9.

Highs School is years 10-11-12.

This is in terms for a two-school system, where it's 6 years per school type (Primary/Elementary and High).

The normal age for year 7s is 12-13. A first year in highschool should be around 15-16.

Akemi is 18. Or should be. 17 is also acceptable.