Age Gap Concern

For people worried about this, I don't think you have much to worry about.

If I remember correctly, they really aren't that far in age. It's just that she carries herself with more maturity — which makes sense given her responsibilities.
I think, and I really hope I'm not wrong about it, in a chapter when we were moving through Jisuk's arc near the beginning, didn't they have a chapter where it shows him and Jiyoung in school as kids?
Assuming it's not an escalator school where all the grades are smooshed together throughout a series of buildings, then it means their grades aren't far apart. Maybe, like, 3-5 years?