By Mary Gahan BBC News Online business reporter

The way in which countries plan to look after elderly people will have to change because of the ageing global population, according to the United Nations (UN).

It estimates that by the middle of this century the number of elderly people in the world will outnumber children.

Delegates from nearly 200 countries are attending a UN conference in Madrid this week to try to find solutions to the problems posed by the ageing population.

The age trap

Average age 2001: 26 years 2050: 35 years Over 60s 2001: 600 million 2050: 2 billion Source: United Nations

As the number of retired people grows, it will become increasingly difficult for governments to find the money needed to pay for health care and pensions for the elderly.

If benefits are to be maintained, those who are working will have to bear more of the cost.

Early retirement

The fastest-growing section of the world's population is the oldest one - those people aged 80 and above.

It will cost more to provide pensions and health care for an ageing population

At the moment this group numbers more than 70 million, but over the next 50 years it is projected to grow to five times that number.

The UN says Italy has the world's oldest population, with a quarter of people aged over 60.

It is closely followed by Japan, Germany & Greece, where over 60s make up 24% of the population.

The UN warns that as the world's population continues to age, we will all have to find new ways of living, working and caring for each other.

In the developed world, early retirement has become a trend but it might no longer be a realistic option for the majority of people.

Workers in the UK and other industrialised countries are already being warned they need to save and invest in pensions because they will not be able to rely on state benefits in the future.

Older workers

Allowing workers to stay in their jobs beyond a standard retirement age would improve their income and reduce the pressure on pensions and social security benefits.

The image of older people as unproductive, dependent and subject to irreversible decline, needs to be shattered

United Nations

For that to happen, many companies will have to change the way they regard age

According to the UK charity Age Concern, there are still widespread misconceptions about the abilities of older workers.

It says it is a myth that older people are slower to adopt new technology and more resistant to changes in work practices.

Voluntary work

For workers whose jobs involve heavy labour, working beyond 60 or 65 might simply not be possible.

Elderly people's skills could be harnessed

But those who have retired can still make a valuable contribution, according to the UN.

It says countries should encourage those who have retired to do voluntary work so they can become more involved in the community and in society.

As well as being able to use their skills, people who stay active are more likely to stay fit and well, so they will be less of a burden on the health service.

Living in poverty

The growing numbers of elderly people in developing countries face different problems.

The UN says population ageing poses a challenge

Poorer countries have not built up the sort of health or care services needed to cope with a population which lives longer.

In such countries, older people could end up living in poverty without proper access to basic care or the right sort of food.

According to the UN, population ageing is not a catastrophe, but it does pose a challenge.

It says that since ageing is a long-term phenomenon, there is sufficient time available for mechanisms to be introduced to help reduce the problem.