Not only is the population ageing (like in Japan and the US), but birth rates are falling and women are increasingly less inclined to get married.
In 2013, the country’s birth rate plummeted to the lowest level on record: only 8.6 babies per 1,000 South Koreans were born, and the total number of births fell by 9.9% to the second lowest number on record.
“A 2014 study commissioned by the national legislature concluded that South Koreans could ‘face natural extinction by 2750 if the birthrate were maintained at 1.19 children per woman — assuming no reunification with North Korea or significant inflow of migrants,” according to the Brookings Institute, citing data from a simulation commissioned by the National Assembly in Seoul.
According to that simulation, South Korea’s current population of 50.2 million could fall to 20 million by the end of the century. The second largest city, Busan, will “go extinct” by 2413, while the capital, Seoul, will go by 2505
I don't believe this for a second but slay if this is true, Korea doing their part for population control 
