>>280795949What she uses to refer to him in Japanese here is "Miseinen," which is usually meant to refer to someone who's less than drinking age (20) rather than less than legal fucking age (16, though I think it can be higher in some prefectures?)
Kana's 21 in main manga continuity (birthday is on November 9th, who knows if this spinoff is starting before or after that) so she's got as many as 4-5 years on him but could also only be a little over a year older (pic related was in summer, for all we know he turned 20 a week later.)