There is this fluffy Thai romance drama, Lovey Dovey (2016). It was based on a famous novel Lovey Brother and Dovey Sister. The other lead couple has an older guy and younger girl relationship. He was a twelfth grader (18 y/o maybe?) and she was just 10 years old when they first met years ago, wherein he was smitten by her cuteness and liked her instantly but he never came anywhere near her nor actively pursue her until she turned 18. In fact, he finished his studies in the US before coming back to Thailand. The other lead couple is the younger girl's super protective, feisty older sister (she's the best friend of the older guy as well) and the older guy's younger brother (younger guy-older woman relationship).