im not an expert in sexual development so i can't say it's impossible for people under the general age range that puberty hits to not get aroused, but people only contract the "disease" when they're infected by a parasite that's passed through mucous. therefore even if you were an adult, you are still safe if you don't get exposed to infected body fluids. that's why the mc's best friend stayed a normal human the whole time (until the time leap bc we don't know where he is at that point).
also, even if you do contract the parasite, there's no guarantee you'll become a libidor (iirc libidor was used to describe people who could control the parasite and didn't turn into mindless monsters). i don't recall them describing the factors to become one yet though so i can't really expand on this.
Wait, so kids are safe from becoming Libidors since they haven't hit puberty= no libido, even if they're attacked (by a pedo libidor)??