I know that in japan and other countries it's not like that, but in my country, 13-18 is acutally highschool age (obv 13 being a 1st year and 18 last year)
Now, some might say that it's pedo...and i understand, society tell us that if you're 13 you're a kid and if you're 18 you're a grown ass adult...but 5 years is not that big of a gap
If he was 38 i'd understand, they could be father and daughter, but it's not like they're gonna bang on their next "date"....just read about how a girl and a boy will probably fall in love without having other thoughts