Park Jae-yeol sorts his packages prior to delivering them, at an apartment complex in Seoul. Picture: AFP/ Ed Jones

Seoul - In theory Park Jae-yeol should have retired 11 years ago. But despite its advanced economy South Korean state pensions are meagre, and the 71-year-old is obliged to continue working, delivering packages to high-rise apartments.

He pushes a cartload of brown boxes into a lift at a block of flats in Seoul, his ageing eyes strained by constant squinting at tiny address labels.

"Money is the biggest reason" he is still working, Park told AFP.

He is one of millions of elderly South Koreans pushed into labour well past the official retirement age of 60. 

Social safety nets in the rapidly-ageing country are weak, despite South Korea ranking in the OCED club of developed countries.

More than 45 percent of elderly South Koreans live in relative poverty -- less than half of the median household income -- by far the highest proportion in the OECD, where the average is 12.5 percent. 

- 'Until I'm 80' -

Park is one of millions whose efforts powered the "Miracle on the Han", the country's transformation from a war-ravaged ruin in the 1950s to the world's 11th-largest economy.

A high school graduate from the southern port of Busan, he worked in air conditioning maintenance, earning enough to raise three children and buy an apartment in Seoul. 

He formed his own air conditioning servicing company, but like many people of his age was never able to build up a cushion of savings for his twilight years.

"Our generation was too busy just trying to survive and raise children during these crazy times, unable to prepare for our post-retirement years," Park said.

South Korea only introduced a national pension scheme in 1988 and it did not become mandatory until 1999. Payouts are dependent on the amount and duration of contributions, with a 10-year minimum.

"Many of those in their 70s and 80s missed a chance to pay into the system so are left out of pension benefits," said Hwang Nam-hui, a researcher at the Korea Institute for Health and Social Affairs, and must survive on welfare payments that are "ludicrously low".

Park's firm went bankrupt in 2012, leaving him having to rely on a national pension of about $130 (about R1600) a month and an elderly subsidy around $180 (about R2200) -- "nowhere near enough" to live on in one of the world's most expensive cities.  

"That's not even enough for pocket money," he said, adding he did not want to rely on his children to give him monthly allowances. 

So he signed up for a state programme to help the elderly get menial jobs, and started working as a deliveryman in 2014.

He now works three days a week, taking up to 100 packages to their destinations and earning about $500 a month.

Most of his co-workers are in their 70s, with the oldest 78.

Park has already worked for more than five decades, but said he hoped to carry on "as long as my health allows... maybe until I'm 80". 

- 'Silver tsunami' -

South Korea's fertility rate -- the average number of babies women have in their lifetime -- hit a record low of 1.05 last year, far below the replacement rate of 2.1.

Over-65s are expected to make up 25 percent of the population by 2030 -- a phenomenon dubbed the "silver tsunami".

In the past, traditional extended family structures, with three generations living under one roof, ensured the elderly a life of relative comfort with support from their offspring, researcher Hwang told AFP.

But the radical social changes of recent decades have seen filial obligations wane, and the elderly forced to remain in work.

Statistics released in March showed more South Koreans in their 60s were economically active -- either employed or seeking a job -- than those in their 20s. 

Park and his 63-year-old wife -- who works as a convenience store cashier -- take only one week off a year, to go to the resort island of Jeju.

But, Park insists: "I feel so grateful and lucky to still be able to work."