Hampshire and the Isle of Wight are both set to see their populations of over-50s rise rapidly over the next 20 years, research for the BBC has found.
The island has the UK's second highest concentration of over-50s (45%) with the figure set to rise to 51% by 2029.
Hampshire's over-50 population is set to rise to 44% by 2029 pushing its UK ranking from 58th to 28th.
The research by Experian looks at how areas of England will be affected by an increasing ageing population.
The Isle of Wight is ranked only behind Dorset (47%) for the highest concentration of over-50s among areas across the UK.
At the bottom of the list were the London Boroughs of Tower Hamlets (16%), Lambeth (19%) and Wandsworth (20%).
The statistics also show the New Forest is seeing one of the biggest migrations of over-65s with about 800 people setting up home there last year.
The area saw the joint fifth highest influx of over-65s across England and Wales.
The highest was Wiltshire which saw about 1,300 new arrivals over the age bracket and Cornwall with about 1,200.
Dr Athina Vlachantoni, who lecturers on ageing and population change at the University of Southampton, said an ageing population could pose problems for councils.
She added: "Although the combination of higher numbers of older people and the expected cutbacks in council services will of course place greater pressure on councils... there are two issues to bare in mind.
"Firstly, not all people aged 50 and over require care, indeed about 50%... report having 'good' health and are not likely to require social care.
"And secondly, councils need to have a better understanding of the circumstances of people aged 50 and over, particularly their living arrangements and the extent to which they receive support from friends, family and neighbours.
"For example, one-third of people aged 65 and over provide unpaid care to another family member, usually their spouse."