I mean in canon she's the only student who's 18 year's old so she's technically an adult, and this could happened in the other universe with sensei married kayako and had kids together.
I mean in canon she's the only student who's 18 year's old
Wakamo is also 18 and while Shun's official age is unknown she's at least old enough according to Kivotos' law to drink alcohol. Also according to Kirino StudentXTeacher relationships are legal too. And then there's all the still unplayable students whose ages are unknown.
