The report pointed to data obtained under the Freedom of Information Act from NHS England which showed there were more than 1.7 million 12-hour waits in 2024-25 at major hospitals – around one in 10 of those who attended A&Es.
Two thirds of them were experienced by people aged over 60.
The report said as well as being horrible, long waits were risky.
Age UK director Caroline Abrahams said it was a "crisis hiding in plain sight" and that the government should take immediate action.
"No-one should have to spend their final days in a hospital corridor where it's impossible for staff to provide good, compassionate care.
"As we head into winter, we fear that an already difficult situation will get worse.
"Long waits are like a rot eating away at the heart of the NHS, undermining public trust."
Age UK said a major cause of the problem was the lack of available support in the community, which meant hospitals could not discharge patients who are medically-fit to leave wards. That results in a shortage of beds available for new patients.
It called for a renewed effort and drive to tackle this.
RCN general secretary Prof Nicola Ranger said the problems were a "moral stain" on the health service.
"No elderly or vulnerable person should be forced to endure these conditions.
"Overstretched and understaffed nursing teams work hard every day to deliver the best care, but they face an impossible task."
Health minister Karin Smyth said: "No one should receive care in a corridor - it's unacceptable, undignified and we are determined to end it."
She said the government was investing more money in the NHS and detailed data on corridor care would soon be published to hold the system to account.
"To tackle a problem you've got to be honest about it," she added.