This manga does a great job of keeping the characters in character.
Tachibana turned into a bishoujo but he still acting like a middle age salaryman because thats who he was...Not suddenly act cutesy and break character just because he has become a girl.
In japan, anyone over 15 is an old man. But all seriousness aside, ojisan translates to uncle or mister. So maybe old man is simply a poor choice of words by translator?
lol 30 year is old back to the retirement home ya boomers bout to keel over need that monster energy sip of the day?
not me though, I'm forever young, always 17
ain't nobody who can tell me otherwise