The ageing jail population has left prison officers providing care for a growing number of older inmates "dying in front of them", officers have said.
The warning from the Prison Officers' Association (POA) has come as new figures revealed the oldest prisoner in England and Wales was 104 years old.
The data showed there were 13,617 inmates aged above 50 out of a prison population of 82,710 in June 2019.
The Prison Service said it was working to meet the needs of elderly prisoners.
More and more inmates were frail, incontinent or had dementia, the POA said.
"You're looking at young prison staff that are trained to be prison officers that are becoming carers," said Dave, who has worked in prisons as a custodial manager for more than 30 years.
The former officer, who did not want his real name used, said when he started work older prisoners were transferred to less secure jails when they approached the end of their sentences but that had changed.
"Now you're getting older prisoners starting big sentences and the young prison officers are coming straight from university, with very, very little life experience and then they're having to deal with major traumatic events like somebody dying in front of them or caring for somebody that is at the end of their life."
His concerns were echoed by the chief inspector of prisons, Peter Clarke, who said the Prison Service should consider whether a new type of accommodation was needed, specifically designed to deal with older prisoners.
"It feels to me as if they're trying to shoehorn this problem into existing accommodation instead of thinking more radically," Mr Clarke said.
The ex-prisoner's view
Ken Denton, from West Yorkshire, was released from prison in June after serving a sentence for fraud and threats to kill. Aged 53, he was housed in an over-50s wing at a Yorkshire prison.
"When you look at some of the prisons, you know, they're three or four landings high, thin ladder stairways, how do you expect an elderly person to climb them?
"When they come in, you are assessed and they'll say well you should be located 'flat' but if there's no space where you going to put somebody? How can you put somebody at second or third landing? You can't, it's inhumane.
"I saw people with cancer, saw people with diabetes, long term prisoners that need their medication but can't get to their medication because the medication hatch is on the second floor and they've got to go to a lift but they can't get into the lift because there's no staff to take them.
"If you needed a wheelchair, it might take you three to four months to get a wheelchair because one had to be designed for yourself and it also had to come from the specific local authority in the area you came from."
The Prison Service said: "An ageing prison population poses particular challenges, which is why we work closely with local councils and healthcare providers to make sure we meet the needs of elderly prisoners.
"Last year, a report by the chief inspector of prisons found there was good work ongoing to adapt prisons for older inmates, and we have updated guidance for governors on how to best support them."
However, national chair of the POA, Mark Fairhurst, said the system was failing to meet the needs of elderly inmates.
"We need more disabled access cells situated at ground floor level. We need 24-hour healthcare and we need proper training for staff."
Analysis - The ageing prison population
The number of prisoners over the age of 50 has almost tripled from 4,824 in 2002, the point at which comparable records start, to 13,617 in 2019.
The overall prison population in England and Wales has risen 16% in that time.
About 16% of prisoners were over the age of 50 as of June 2019, compared with just 7% in 2002.
The figures showed that of the 13,617 over 50s, 1,759 were at least 70.
Women made up 548 of the over 50s prisoners, including 32 aged 70 and over.
People in their 30s are still the largest age group in prison, making up just under a third of the overall population.
Tougher prison sentences and the rise in the number of those convicted of historic sexual offences are believed to be part of the reason for the ageing prison population.
In 2016, 101-year-old Ralph Clarke was jailed for 13 years for committing 30 child sex offences dating from the 1970s and 80s. He was believed to be the oldest person convicted in British legal history.
Dr Mary Turner, reader in health services research at Huddersfield University, said: "People tend to get longer sentences, even in older age, now than they might have done in the past and there are now more older people going into prison than there are being released."
She said the situation was not sustainable.
"We can't just see these numbers going up and up and trying to cope with it in a prison environment so we're going to get to a point where we have to think of alternatives and we have to find solutions."
She said options could include building secure care homes and considering alternatives to custodial sentence for older offenders.
Peter Clarke warned the number of men over 50 being held in jails would rise to more than 14,000 by 2022, representing 17% of the prison population.
"The Prison Service has so far has said that it's not going to develop an overall strategy to deal with this issue," the chief inspector of prisons said.
"When prisoners get older, less capable physically or infirm, they don't provide an escape risk, they still have to be held in custody very often and it's not to say they wouldn't present a risk to the public if they were completely at liberty.
"But the question is do they need to be held still in levels of security which are not needed for their physical capabilities and which inevitably are very expensive as well?"