i think it's because of the difference in language expressions. so from kr to eng translation team went with the literal meaning of the text, but it sounds weird in english.. so the "secondary sexual characteristics" probably meant hitting puberty in that context :)
"Secondary sexual characteristics" doesn't refer to omegaverse, it refers to features associated with one's sex that aren't directly part of reproduction. Like beards and boobs
Im so confused is this omegaverse??? Theres no tag of omegaverse but theres a secondary characters or whatever