[Warning: Slight spoilers for volume 5 of the ZnT manga ahead.]
Well, Hakaze's age hasn't been confirmed for good so far. There's only been a few hints:
- She's supposed to be older than Yoshino and Mahiro, and the age difference apparently isn't only a year or two (in volume 5 of the manga, she chides herself for "behaving like a teenage girl with a crush").
- She's also younger than Junichiro (the two of them refer to each other as "little sister"/"older brother" ("Jun-nii") respectively; also, there's an instant where Junichiro drops a few lines about Hakaze as a child). Now Junichiro's actual age hasn't been confirmed either, but he is a college student, a.k.a. in all probability somewhere in his twenties.
Personally, I'd think Hakaze would be about 19-20, but as I said before, it's just an estimate, and her actual age still has to be confirmed.
Doesn't look like it to me, frankly said. They've been switching the order of quite a few scenes for the anime adaption, but I suppose that's for directional purposes... haven't been seeing major differences, at least.