The big question is...do Fuuka and Mr. Koiwai pass the 10 Year Rule?
My personal opinion is that, even with his daughter, Mr. Koiwai is young and just striking out on his own. Sloppy (and very young bachelor-like) personal habits, not many possessions, only just recently got his own place, has a job that would likely go to a relatively recent college grad...
Plus, looking at his two friends...we have one who seems to be about the same age who works the family business and still seems to live at home, and another who is a bit younger and appears to be fresh out of school and working an extremely entry-level salaryman job...and can barely afford ramen...
I bet even 25 years old is pushing it for Mr. Koiwai.