And I totally agree here. Beside the older LI in the game, the older students are 20-21 (like Sage, Heather, Rusty, Tommy, ambiguous for Lily, etc.), while most are between 18 and 20.
I'm -way- older than that, but I remember that I didn't know what I wanted when I was that age.
And I think that's one of the points of BaDIK, they don't know what they're doing...
Zoey was the first best friend the MC ever had, and I think it was likewise for Zoey, they discovered their puberty and sexuality together, for a span between 4 to 6 years, they were each other's LI, but they didn't know what they were doing... before she left cause she didn't know what to do with her life, she wanted the MC to come with her, because she couldn't see it otherwise. The MC didn't know how to react, but he wanted to finish school, so he stayed behind... you can see in Interlude how Zoey thought she had it all figured, going to chase her dream, while in reality she didn't know what she was doing at all, moreover, she left the one she finally figured she loved behind, and they even cut their contacts... while the MC 'got over it' and tried for something else instead.
They didn't know what they were doing, of course, they were 18 when Zoey left.
Same pattern comes back with the throuple, Josy got a crush on the MC because she didn't know how to repair the gap between her and Maya, and the MC made her feel good again. Maya developed feelings for the MC, but didn't understand why cause she thought she was lesbian (just to clarify, a real lesbian couldn't fuck a man without help, in Ep8 she doesn't need that help, beside alcool, at the dorm, my little brother is gay and before he admitted it when he was 18, he tried a couple times with girls, never worked) and went on because the MC made her feel good. And then when the MC and Maya/Josy choose to try something, they admittedly don't know what they're doing, but they try it anyway.
Sage was scared to date the MC because she doesn't know what a real relationship is and didn't want to lose him. Her family is fucked up and she doesn't know how to deal with her feelings.
Jill doesn't know what dating is at all, and never had any sexual experience. She was always imposed things, she never really decided on her own, for her own life.
Quinn (bla bla bla I hate her bla bla bla, get over it thanks) doesn't know what healthy feelings are at all, fucked up upbringing, dead father, wrecked mother who doesn't recognize her anymore... she doesn't know anything about dating, at all either.
Derek seems to have an answer to everything, but the rare occasions where he isn't goofing around, you see he doesn't have a clue about what he's supposed to do, his feelings for Ashley being the first major thing.
And so on and on and on...
They're between 18-22 for the most part, of course they don't know.
One thing though, brought that aspect a couple times already, but the MC is an introvert, the way he process information, the way he's pretty much always listening and in his head more than talking and being the center of attention. Maya is an introvert, Sage also is (yeah she's partying without problems, but most of the time, she's alone), Bella is, too. I'm an introvert, I'm sure there are introverts here, heck I'm sure DPC is an introvert himself, an extrovert can't really know how an introvert works inside (not a knock on extrovert, just to be sure).
Where I'm going with that, is what Zoey represents to the MC. When he told his backstory to Bella, while I wasn't bullied like he was nor was as dirt poor, I understood what he went through. When someone, like Zoey, comes into your life as a youngster, and manages to get you out of your bubble, that person suddenly becomes -very- meaningful.
She meant the world to him.
I wouldn't even be surprised if Zoey is a reference to one of DPCs own childhood friend/crush, that he went through something similar the MC lived. He worked way too much on her for her to just be an afterthought in the MCs life.
That's why he had an existential crisis on that bench, when she left.
That's also why he had an existential crisis when Neil called him at the end of the Interlude.
He just made a choice, but the 'love of his life', who left about 6 months ago, is coming back, a recent past which hurt him (because of a huge misunderstanding), but someone he just can't brush off, even with the choice he made.
Cause let's be honest, as its been said since the start, teens don't know what they're doing.
Zoey will be the test of his young life so far.