there's no age gap in IOTNBO but in both dramas:
- the FL is rich (and has a great wardrobe) + has been sheltered (personalities differ though)
- FL pursues ML first and relentlessly chases after him
- has a ML who has things holding him back from starting a relationship with FL (in TFF its age gap and his responsibility as an adult, in IOTNBO its his responsibilities and her personality).
- both have great chemistry between leads
other than that plot varies wildly, but I think it's a good rec to keep in mind if you run out of directly similar ones.