Its not the same everywhere? Pretty sure they knew their secondary pretty young if only you had read the earlier chapters
What?? If you're talking about rules from another omegaverse, then those rules don't apply here. Omegaverse is a whole other fictional universe, every omegaverse author has different rules other than the main point of secondary genders. I'm also not sure if you tried saying Su-ah made Juhyeok an omega here, so if you were, he didn't. Juhyeok's family made him an omega, as his family was full of alphas, even if Su-ah was dead or sum, Juhyeok would've turned into an omega, because of his family. It had to be prolonged explosion to alpha pheromones, but Juhyeok and Su-ah were too young for their pheromones to be too powerful, if you reread the chapter, even Juhyeok's mom said, "ofcourse he's been exposed to alpha pheremones! Our whole family is made up of alphas!" or something along the lines of that.
How did he smell an omega when they get their secondary gender at 16? Bro was in elementary school so he would still be friends with the ml so hes not an omega yet. Does the writer even know what they said?