I mean, according to the numbers, the range is 1-5 years apart.
1. the minimum (1 year apart) if Kagari is 9th(3rd grade of middle school) and Nana is 10th (1st grade of high school).
This is the least likely since Yae is younger than Nana but 1 year older than Kagari (what was I even thinking -_-'). 2 years apart minimum might be more plausible if we count Yae in.
2. the maximum (5 year apart) if Kagari is 7th(1st grade of middle school) and Nana is 12th (3rd grade of high school). I like this one better since it makes sense according to Nana's age concern.
the problem is, if currently Yae is 12th grade, and Kagari is 11th, that means its been 4 years since Nana graduated highschool. The average time spent for university is also 4 years, so by that logic Nana should have just get a job, and not a senior at his workplace (unless he spent less than 4 year at Uni, or he didnt go to uni at all, then it make sense 👍)
3. it can be wider or closer, since some people can get into school too early (younger than their peers) or too late (older than their peers)
