Ok so considering how you said preferably complete i will divide the two.( It's pretty small since i haven't read that many bls with an age gap that i can remember). Completed 1. Assistant Architect- So this is one I'm currently reading and it is about this guy called Zhang Siyi who just finished his studies overseas and is back in China looking for a job as an architecture. The job he lands is what the story most entails about . The book is a bit slow paced and the age difference is about 8 years. 2.Rebirth of a Movie Star : This is a reincarnation about this small movie star. I think it really great because his main focus isn't on getting revenge like a lot of leads hope to do when reincarnated.I can't remember how much of an age difference there is between the two leads 3.Your Distance is a story with a system similar to Love Alarm/Dice ( the Webtoon). Not in that they can feel the distance of a lover or enemy but that they can see the distance of the person they choose on a dating app ( think tinder IG).I think one of the aspects i love about this story is anonymity is not the main conflict ( you are not constantly waiting to see the two realize who's who . Instead it is used as comedic relief ). ( It also has a manga ) 4.My Husband is Suffering from a Terminal Illness- I can't remember how much apart they are in age but the story is about this guy who is recarinated as a young idol who is secretly married to the villain of the story. This book is slow paced . 5.Everyone thinks I like him(I'll be honest and admit this isnt an age gap novel but i decided to place this here since it fits all the other recommendations and just incase you need something to experiment if you can't find any more novels at the moment).The story is a highschool setting and the concept of don't misunderstand it is not that i like you which is interrupted as them being a tsundere. The mc has always been second place . I wouldn't really say he had any feelings whether good or bad to the ml. ( If you were ever a fan of The Demon King thinks I like him, and stopped because of the way the story shifted from a sweet narrative midway. Everyone thinks I like you is a story that gives you a nice feeling even after you finish reading it) ( I can't remember any other completed ones right now off the top of my head). Incomplete 1.How to Say I Love You: This is a story i will forever talk about because it is such a fuffly in my opinion.To summarize the story is about a Film Emperor who gains the ability to read minds. Through this ability he learns that there is this guy who he had misperception about .( If you have ever watched the Japanese DramaCherry Magic based on the manga Cherry Magic! Thirty Years of Virginity Can Make You a Wizard?! then it is pretty close to it ). I think there age difference is about 5 year least 10 the most but don't quote me on that . ( I decided not to add anymore because of the fact you prefer complete novels and i don't really remember any others that would keep you coming back except this)