Only a quarter of breadwinners were over 60 years old in 2010, but that is going to rise to about half by 2035. The percentage of single-person households will also rise sharply from 24 percent to 34 percent.

In a report on population projections published Thursday, Statistics Korea said the age of breadwinners will reach 60.9 on average by 2035 as a result of the increase in life expectancy. And single-person households will outnumber married couples due to a rise in the number of elderly shut-ins.

The projections are made every five years.

Married couples with children made up the largest proportion of households at 37 percent in 2010. Next came singles (23.9 percent) and married couples without children (15.4 percent).

But single households will make up the largest proportion at 34.3 percent by 2035, to be followed by married couples without children (22.7 percent) and married couples with children (20.3 percent). The number of elderly shut-ins will likely rise dramatically, with householders in their 70s topping the list at 20 percent, those in their 60s at 17.5 percent, and those over 80 at 16.4 percent.

Population aging and family disintegration are two main reasons for the sharp increase in the number of elderly singles. Nuclear families of three or four were common until only 10 years ago, but families are now being broken down into smaller nuclear units, as more aging parents live separately from their children.

Seo Woon-joo of Statistics Korea said, "Elderly shut-ins could pose a serious social problem" as society ages. Korea is expected to overtake Japan, an aging country in 20 years' time in terms of the percentage of householders over 60.

The ratio of household heads in their 60s to all households will likely more than double from 25.1 percent to 51.2 percent, while that of those in their 30s and younger will drop sharply from 27.6 percent to 14.7 percent, Statistics Korea predicted.

The total number of households will show a 1.3-fold increase from 17.36 million to 22.26 million due to the increase in single-member households, even though the population growth rate will drop below zero after 2030. The average number of household members will fall from 2.7 to 2.2.

In 2010, households led by a 40-something person topped the list at 14.2 percent, but by 2035 the largest proportion will be headed by a person over 70. The number of couples over 85 is expected to increase more than five times from 30,000 to 160,000.