I think the word you're looking for is gross. Besides, Kakashi deserves an actual woman, regardless of what his loving memories of 15 year old Rin might inspire in him.
I'm pretty sure the age of consent in Japan is 16, so it's not AS weird for someone who's 20+ to date someone who is 16+, it's still weird though. For the States.. yeah it'd be taboo and I'm sure Naruto would be banned in some areas that are strict.