Adam's feed

Why is the author being so cagey with that "over 12 years"? If you can't say t with your whole chest, why not make the age gap smaller than 12 years???
It's 15! If he's a 1st year in college and he didn't skip a year to study he's 18. And he's 19 at most anyway, because he wasn't allowed to drink yet!
And this story still would've worked the same if it had been 12 years instead of 15.
Hell, it even would've worked with 8 years.
Anyway, I think the mangaka is a coward