oh yea proof
Rainbow city Manhwa chap 4 when Dr.seok was opening the door to the lab, the screen reveals he is 34 years old
Rainbow city Novel, when Mjaor Kwak goes in the lab to drink with Dr.Seok, it states
"“Major Kwak Soohwan, please verify your identity first.”
He placed his five fingers on the glass door.
<32-year-old Major Kwak Soohwan, Rainbow City>"
So basically, I got every single chapter of Rainbow city on booktoki translated each into a google doc (theres 23 cause booktoki likes to mash them together), I read season 1 of rainbow city manhwa at least 17 times and I got that memorized by heart. Anyways, this one day this person asked me for a summary of the entire rainbow city novel SO, I spent 3 days, starting from right after season 1 on the manhwa, in the novel and explained all the important pieces and events bit by bit, splitting each explanation according to the chapters on booktoki. And thus, I know exactly what chapter has what events that occur and the order of each event that happens to in the novel so I can determine the approximate chapter the event is in. But in this case, I actually specifically tried to look for Major Kwak's age in the novel once and that's how I knew.
Yaoi/Yuri where the characters are older around 30-50 (no age gap both are the same age ish)