I think you're misunderstanding. Protagonist thinks she's around the same age as herself ("p.5 You're about the same age as me, aren't you?") and she's just a 1st year high-schooler.
Very unique style. I'm interested in seeing where this is going, but PLEASE don't be another "I didn't know you were a girl!" manga.
That cover picture is lovely.
Wasn't feeling it reading the previous chapters but this one really closed it out nicely. Curious how the next volume develops since she's finally gotten her closure.