May I remind you that their age gap is very little. Noona's older but she's still young like jiwoo. Maybe they have an age gap of two years or so. It's been said in the first chaps that they only reason why noona's the head is because she's the "oldest-possible-one-available". So no creepiness here, the author already informed us that she's young just like the other kids, she just looks matured coz she had no choice but to be one
then don't read it. You're saying it feels forced when this has been hinted at for a while now and their age gap is 2-3 years which isn't that uncommon in relationships between 16-17 yr olds and 18-19 yr olds. It'd be a different story if noona was 25 or something but she isn't. and given how long they've hinted at it, you can tell its a pretty slow process with no miscommunication issues at all and mutual feelings.
idk but i feel like im reading a forced romance between jiwoo and that noona. it also make me kinda uncomfortable that the girl is a full grown adult and jiwoo being a high schooler like what the fuck