Christchurch in Dorset has the highest concentration of over-75s in the whole of England, research commissioned by the BBC has found.
That age group currently accounts for 16% of the town's population but in 2029 it is predicted the figure will have risen to 20.2%.
In Dorset the over 50s are expected to make up 55% of the population by 2029.
The research by Experian looks at how areas of England will be affected by an increasing ageing population.
It also found that Christchurch was closely followed by many other Dorset areas on the list of the highest concentrations of older people.
In East Dorset over 75s make up 13.7% of people, in west Dorset the figure is 13.4% and in Purbeck it is 11.9%.
Councillor Alan Griffiths, leader of Christchurch Borough Council, said it offered the town a "huge opportunity".
"We have a pool of people who have retired in good health and want to do something constructive with their time and are therefore able to volunteer and contribute to the community," he said.
"People do come to retire here, which of course puts pressure on the housing market, especially as there are few sites for new homes to be built in the borough.
"But we are currently consulting on a proposed urban extension which will provide more homes for our young people to enable them to get a foothold in the housing market.
"We must also remember that the quality of life is so good in Christchurch that people do live a long and happy life here, and we're delighted they do."