4. Dr. Romantic 2 - Graduated from same class showing that they are the same age in the drama but in real life there is 5 years age gap between the actors..
5. Kieta Hatsukoi - Study in the same class in the drama but there is 5 years age gap between the actors.
2. Cute Programmer - the ML's character is older than the FL (I'm pretty sure they are even an age gap couple in the drama), but in real life, the actress who plays the FL is five years older than the lead actor.
3. Sotus - it is not by much, but the ML, Arthit, is the ML, Kongpob's, senior in school by two years. But in real life, the actor who plays Kongpob is a year older than the actor who plays Arthit.
8. The Untamed - Xiao Zhan (playing Wei WuXian) is 9 years older than Wang YiBo (playing Lan WangJi); in the drama, LWJ is asked to sit in on the studying sessions to give a good example to the newbies, implying he's a bit older than the newcomers. He's also the more mature of all the students. In the novel, they're around the same age, though it's not specifically mentioned which one is the older.