Romances with a significant age-gap, especially when one character is just entering adulthood, are tricky business. There's a million ways they can go wrong. A Kiss on Tearful Cheeks serves as one of many examples of what not to do when writing a May-December romance.
Our 17-year old heroine is dating a 24-year old and it takes very little time for her boyfriend to begin to seem creepy and possessive. Neither character in the story has the emotional maturity to handle the relationship and things that are precursors to abuse are treated as romantic. Our heroine is submissive in every way and pretty much lets
her boyfriend do whatever he wants. Meanwhile, the boyfriend's attitude goes beyond a cute level of jealousy like the manga tries to play it off as; at one point, he goes out of town and makes his girlfriend promise not to even leave her house because he doesn't want her around other men.
A Kiss on Tearful Cheeks is every complaint you've heard about age-gap romances brought to life, and is best avoided.