@karolyn makes sense, but I don't know anything about korean colleges so I can't say for sure. Also, if school officials know her age and then see her in person, it's going to be national news. However, I'm sure the author will probably just bury this possibility. Author is probably just making her hide her age so that there can be some dumb drama where someone romantically interested in her finds out her real age. Like I said, I don't care about the logic or plot holes, I just enjoy the story atm.