Kim Hang-gon of the National Police Agency said, "The number of felonies like sexual crimes committed by the elderly has increased because they're healthier and more active than they used to be," righteously or otherwise.

Police are baffled, pointing out that the worst thing the elderly did in the old days was to steal a little firewood or cheat at cards. The number of felony and violent crime suspects per 10,000 elderly population aged over 65 increased from 26 in 2012 to 31 in 2017. That of sex crime suspects soared 91 percent.

The proportion of geriatric criminals committing violent crimes like murder and rape has surged 24 percent per year over the past five years. That was way ahead of the increase rate of the elderly population as a whole at 4.5 percent and six times the overall increase of violent crime at 4.2 percent.

Some blame rapidly changing social standards. The elderly are often used to a rigidly Confucian hierarchy where their seniority is respected, but in a changing society that leaves them without a clearly defined role they become confused and angry. And pent-up anger is increasingly released in violent crime.

Doctors also point out that people become more bigoted and have trouble controlling their anger due to hormonal changes as they get older. The older people get, the less neurohormones like serotonin and dopamine provide them with pleasurable emotions.

Hormonal shifts occur in men and women after they reach their mid-50s, and many lose their emotional balance, especially in an angry society like Korea.

Prof. Yoon Dae-hyun of Seoul National University Hospital said, "The decline in cerebral function as the result of aging also makes it difficult for the elderly to control their anger."

Experts say local communities can play a role in detecting warning signs as many elderly people live alone without warming human contact.

"Seniors are often more rigid in their attitude, which makes it difficult for them to resolve conflict through dialogue," said Kwak Dae-kyung, a professor at Dongguk University. "Police and local officials need to listen to the difficulties of elderly people and step in when needed."

Prof. Han Chang-soo of Korea University's Ansan Hospital said, "It's important for the elderly to work about 20 percent less than before and maintain some physical and emotional reserves, because they have less ability to control their emotions than when they were young."