The population of New South Wales is ageing rapidly, with regional areas seeing the biggest growth in older people, new figures show.

It is predicted that by 2021, there will be more people aged 65 years and older living outside Sydney than under 16s.

The figures are contained in the latest Population Bulletin of the Department of Planning and Environment and coincide with the United Nations National Day of the Older Person.

In the period between 2004 and 2014, the over-65 age group grew the fastest in the South and East Tablelands, where there was a 46 per cent increase.

The Far West saw the slowest growth in the older demographic at 24 per cent.

While Metropolitan Sydney remains relatively young, there has still been a 31 per cent increase in people aged 65 and over.

The department's analysis shows those aged 65 and over are already outnumbering those younger than 16 in the Central Coast, Illawarra-Shoalhaven, North Coast, South East and Tablelands.

That same pattern is predicted for all regions outside Metropolitan Sydney by 2021.

State must 'learn to adapt' to ageing population

New South Wales Planning Minister Rob Stokes said strategies to get younger people to move to or stay in the regions would be vital for the future.

The older demographic in NSW is growing faster than younger people. ( Department of Planning and Environment )

"Transport access, education opportunities as well the mix of jobs that are going to be necessary to inspire people to live outside of Sydney," he said.

Mr Stokes said he was confident good planning could meet the needs of an ageing population with more disabilities.

"[That includes] shorter distance public transport routes, more accessible dwellings, more one and two person units, terraces and apartments," he said.

The minister said family immigration could only play a part in arresting the trend.

"Migrants age too, so in and of itself migration levels are not going to be sufficient to deal with the general ageing trend," he said.

"This [ageing population] is an inexorable trend and it's one of those challenges that as a society we're going to have to learn to adapt to."