She can't be. She in college with Lexi...sharing a dorm room. Makes her same age as Lexi and Erynn and they are three years older than the MC (approx). MC has no tattoo...they dated for '2 years' (dialogue in the game)...he just turned 18 before returning back home to Emily. Makes the MC 16 when he met Iris, going on 17 possibly and Iris 19 going on 20 (as we don't know exact dates of birth...though we have to assume the MC was born after Feb...otherwise if was pre December, he'd be in the next year higher of school..meaning he'd have already left high school and be in college himself.). Have to remember, all this takes place (present time) literally 2 to 3 months before they leave high school. Another case of Nyx trying to fudge the rules of high school kids being in 'school'.
Regardless, that still makes the MC a legal minor which even with an animated scene, is a serious, serious no no. People (and Nyx) can fudge this scene however they like, unfortunately the dialogue presented in the game proves the MC is under 18.