@Kaarme A college dude that is at least 20 (I think he drank), chasing after a middle schooler (at most 14-15) is indeed creepy. But a middle schooler having a crush with a college kid is pretty standard and typical.
What I like in the pre-serialization is how non-chalant and how unconcerned he is of Tsuyu's affection. He may or may not realize she likes him, but he just treated her like a little sister and humor her cuteness, which is what makes the dynamic interesting, and it works because of the age gap. If the series "need" to end with them being a couple, they could just end it while after 3 years passed when Tsuyu is about to or just graduated high school. 5-6 years gap is normal for adults after all.
I just think making the guy a high schooler ruined one of the foundation of the pre-serialization... Anytime he is acting adult-like the way he does in the pre-serialization, it will come across as a kid trying to act cool. But that's just my mileage, others might think differently.