He's a classmate of Jayce and John, shouldn't he be their age?
People do skip grades. But I think in this case it's just he is currently 17 where as Jayce and John are 18. So at the moment in time where the routes are available. He is underaged. Monchi doesn't seem keen on making him an option. That is all.
(And yes while the legal age for sex can be 16 in some countries. Advertising it in a VN is a no go. Because it's pornographic. Unless you want his route to be only sweet and no steamy CG's later on down the track... AFTER he has a birthday... ya buncha lewds. :P )