Romance Baby-faced Beauty I Love Lee Tae Ri Flower Boy Ramen Shop Oh! My Lady Big High School King of Savvy Land Of Rain Secret Love Affair Biscuit Teacher and Star Candy The Lover
I would definitely second Witch's Romance, Dalja's Spring and Secret Love Affair, which is one of my all time favourites. I can also recommend What's up Fox and the Japanese Kimi Wa Petto.
This is my favorite trope withing any Asian Drama. I have collected a list that I do try to keep as up to date as possible of younger man/older woman dramas. Here's what I have so far! https://thedramanoona.wordpress.com/the-noona-meter/