Responses
Neither of u are technically wrong. Both middle schoolers and high schoolers can wear gakuran. Its more common for middle schoolers, however. Depends on the school. He was a highschool senior/last year when they met so presumably 17/18 years old. For my sanity, I just assume Kitayama was a college freshman/first year when they met (so 18/19 years old).

Am I the only one that noticed that the one begging for sex is in middle school while the guy with black hair is obviously olderΣ(  ̄□ ̄||)