@GreenDragonSage I think the age gap in many cultures isn't shocking per say, but would still be considered significant, and this is usually noticed more when the woman is the older one. That said, I think the premise of the story is less on the actual gap itself, but more where each character is in life with that gap. The FL is at an age where, especially in Asian cultures, she'd be facing a lot of pressure to marry soon and settle down. On the other hand, the ML is just coming out of high school and starting his youth. He's also involved with a band which I'm sure will add on it's own drama to the story.
Essentially, the main issue is the difference in expectations on them. For her, since she would be having marriage in mind, most would rule out a 19 yr old as usually they aren't looking to settle down yet. Also while they are adults, 19 isn't even old enough to drink over there so she still might be looked at as an adult dating a kid (not in a legal way but societal view). Moreover, family/friends would likely look down on being in a band as it's not considered a stable job and puts his relationships under a spotlight. For him, he'd have the pressures of being in a band which usually wants to avoid the scandal's of relationships when they're starting out. Add to that the stress of transitioning to adult life, especially compared to the guys around the FL's age we'll be bound to meet.
I'm also not sure on how far I'll read this but at least it's intrigued me a bit.