Korean version is the original.
Based on the 2014 Korean film, "Miss Granny," (Susan-han Geunnyeo) starring Shim Enkyung (b.1989) in the lead role. Other versions include the 2016 Japanese remake, "Sing My Life," (Ayashii Kanojo).
When the grandmother played by 70-year-old Ya-Lei Kuei sits down at the bus stop after turning down her son's request to join him in the car, the backlit display she sits in front of prominently features a blown-up image in triptych of Korean actress, Shim Eunkyung, as an ostensible product advertisement. In the bottom right-hand corner of the advert, however, is written in Korean Hangeul, "Soosang-han Geunyeo," which is the Korean title of the original 2014 Korean movie this movie is a remake of.
The Chinese-language title of "20 Once Again" is "Chong Fan Ershi Sui."