Older male younger female age gap (of 15 or more years) romance

https://mydramalist.com/26748-sa-kao-duen (ML is a highly place official and FL is a school girl)

https://mydramalist.com/20578-nang-ai (ML is an ambassador/consul and FL is a school girl)

https://mydramalist.com/11436-tarm-ruk-keun-jai (ML's sister is in love with a guy who is very much older than her)

https://mydramalist.com/24113-mussaya (ML is an army captain and FL is a school girl)

https://mydramalist.com/10034-awayjee-see-chompoo

https://mydramalist.com/16551-hello-mr.-right

https://mydramalist.com/10754-pleng-see-rong

https://mydramalist.com/10195-kularb-rai-glai-ruk(Second lead couple)

https://mydramalist.com/22882-tawan-yor-saeng

try Touch (2020) kdrama. But the romance comes in 5 episodes before the ending. still a good watch tho. Check out my age gap list for more

Itaewon class has 10 year age gap. Highly recommended