The number of elderly citizens in Seoul has surpassed that of young people for the first time since the city started compiling the data, sparking concerns over the fast-aging society.

According to a report released by the Seoul Metropolitan Government on Thursday, the number of those aged 65 or older reached 1.24 million as of last month, about 5,000 more than the number of youth aged under 15.

The aging index also hit a record high of 100.4 points, exceeding 100 points for the first time, the city said.

The index indicates the level of an aging society. Over 100 points suggests the number of elderly citizens who are economically dependent is increasing faster than those who are economically active.

The capital’s aging index has been on the rise since 1996. The indicator stood at 21.8 points in 1996, but surged to 90 points by 2013.

Seoul, which has a population of 10.3 million, is not the only aging municipality in South Korea. The country’s average aging index was 92.2 points this year, more than double that of 2003. The sharp rise appears to be related to the fast growth of the elderly population and declining birthrate, the city noted.

In the past four months, the number of senior citizens increased by about 21,000, while youth numbers dropped by 19,000, it added.

As the aging continues, the average age of Seoul City’s population rose to 40.2 this year, passing 40 for the first time, authorities said.

The average age of residents in one district in Jung-gu was 51 years old, marking the oldest figure in the capital, they added.

“If the current trend continues, 14 percent of the city’s population will be elderly by 2028, leading to an aged society,” officials said.

A city with over 14 percent of those aged 65 or older is considered an “aged society,” and over 20 percent a “post-aged society.” If the elderly population accounts for more than 7 percent, it is called an “aging society.”

By Lee Hyun-jeong (rene@heraldcorp.com)