高1 こういち
kōichi

Noun

1. first year of high school; first-year high school student

Abbreviation
それが こう1の ときだから17年 ねん ちました。
sorega kōichino tokidakara jū nananenga tachimashita.
That was when I was in the first year at high school, so 17 years have passed since then.
Other forms: