Gloucestershire has one of the highest concentrations of older people living in the west of England, second only to Somerset, research for the BBC shows.
The research by Experian showed over-50s made up 38.1% of the county's residents - with Somerset top at 41.8%.
County council chief executive Pete Bungard said Gloucestershire's growing ageing proportion was its "biggest budget growth pressure".
He said looking after older people in 2010-11 would cost about £72m.
The county council said that over the past 15 years the population of people aged 65 and over had seen the greatest increase.
It expects that by 2026, the population of the county aged 65 and above will have increased by 52.7% with people aged over 85 rising by 79.1%.
The population in the county is currently estimated to be almost 600,000.
Mr Bungard said: "We will be supporting 70% more customers at a time when government funding is reducing and our priority will continue to be protecting the most vulnerable.
"It's vital to ensure we have a fair system in place that means people with similar levels of need get similar levels of support."
Julius Marstrand, from the Gloucestershire Older Persons' Association, said: "Gloucestershire has been a reasonably affluent county for a long time, so a high proportion of its population lives longer than the average in less affluent, urban areas.
"It is also a beautiful rural county, so people like to retire here and over the years there has been an influx of older people, over and above those who grew up here.
"As people live longer, over 12,000 people in Gloucestershire aged 65 or over find themselves having to care for partners, or even older parents.
"Many over 50-year-olds find themselves looking after both ageing parents and children at the same time.
"The current generation of pensioners are, on average, better off, relative to the rest of the population than ever before."
Mr Marstrand said older people today expected and deserved to be looked after.