Nicholas Crace said he decided after his wife died last year to try to help someone else with a donation, The Guardian reported. He was too old to donate bone marrow so he settled on a kidney.
"I would have been very disappointed if I had been turned down," he said. "I was ideally placed to be a donor after the hospital had established that I was fit and had excellent kidneys. One can live perfectly happily with only one kidney -- in fact some people are born with only one."
Crace is believed to be the country's oldest "altruistic donor," someone who gives up a kidney to a stranger, the newspaper said.
The process took more than six months, with many trips from Crace's home in Overton, Hampshire, to Portsmouth, for tests and finally a 3-hour operation. Crace said the recovery was quick and he was riding his bicycle within three days.
In an interview with the BBC, Crace said doctors described his kidneys as "Formula One," notably healthy for a man his age.