Teenager's gonna teenage (well, they are a bit older, but you get the feeling...).
No, I think they're teenagers. Mid-to-late, 15-16?
I'd thought they started the story at 16-ish and must be 17 or 18 by now, but yeah, still definitely teenagers. Evie is technically older, but she would've experienced an immediate and premature puberty if her brain chemistry matched her mental age, so she's definitely got a teenager's raging hormones. Though, speaking as someone whose first time was in her 20s...age is merely an exacerbating factor on the immediate and barely controllable horniness from having sex for the first time with someone you love, not a prerequisite~