According to the earliest spoiler here (the one that I assume MTLd a Korean review, age gap is apparently 5 years. I mean, in his POV or at least on the spoiler summary, she views him as a younger brother figure.
SPOILER REQUESTS
1. What does ML do to prevent future suitors given the synopsis mention he just outright tells the other party that MC favors his face?
2. How does the ML convince MCs family to get engaged to her?
3. MLs relationship with the brother? If ML ran to her home for refuge/treatment, then why was MC the villainess?
4. The other prince? OGbody's supposed to be husband in the novel?
5. Why is MC proficient in H2H combat? or at least physically strong?
6. When did MC reincarnate into that body honestly? The fact the guards aren't surprise with her late night travels, her maid isn't questioning a change in attitude?
7. How about the King? Do we have a bastard for a father in law?
8. Reason for reincarnation? Given the first mega spoiler post mention some relevance?
8.5 do we get magic worldbuilding?
9. How does MC fall for ML?
TBA
10. Killian spoilers? I am oddly fond of his character despite of his current number of appearance. An assassin for hire but spares MC simply because he finds her fascinating. Heck, MC being rightfully cautious is just pure plus point in character and development