Parts of Sussex face severe challenges posed by an ageing population, BBC-commissioned research suggests.
The study, carried out by Experian, found the percentage of people aged over 50 living in Rother is set to rise from 51% to 58% by 2029.
It currently has the third highest concentration of over 50s in England.
Age Concern Eastbourne said the booming older population had foreseen in the 1980s but there had been "very little preparation".
The researchers looked at data for district and unitary authorities in England.
In West Sussex, about 47% of the population in Arun are aged over 50, rising to a predicted 54% by 2029, the 11th highest in England.
The number of older people who are economically inactive in Crawley, Eastbourne and Adur stands at about 70%.
In Rother, about a third of pensioners do not have access to a car, while the figure is also high in Arun, Eastbourne and Chichester.
John Barker, the information officer with Age Concern Eastbourne, said the current system of social care was out of date.
He said: "It has been clear from the late 1980s that the demographics were going to change significantly early in the current century.
"But very little preparation was made in the way of creating reserves to support future pensioners before they outnumbered the working population."
Mr Barker said the challenges included engaging older people in activities to help them sustain physical and mental health.
He said more good quality care homes at affordable prices were needed, as well as improved facilities for people with mental illnesses.
In addition, people should be given adequate support to remain in their homes for as long as possible.
"We did not plan for World War II but in the end we won it, and just like then it will take a lot of blood, guts and determination," he said.