Fauja Singh, nicknamed the "Turbaned Tornado", began running at age 89 and has since completed nine marathons. But he admitted that age has finally caught up with him.
"I am hurt by the fact that I am going to retire," the Indian-born British national, who only speaks Punjabi, said in Hong Kong through his interpreter ahead of his final race this Sunday.
"I do not really want to hear the word 'retire' because I can still run and jump on a bus. It's a (sense of) negativity that I have never experienced before."
Singh, who was a farmer in his home state of Punjab in India before settling in England, has competed in nine 26-mile (42-kilometre) marathons in London, Toronto and New York.
His best time was in Toronto, where he clocked five hours, 40 minutes and four seconds.
On Sunday the runner, who turns 102 on April 1, will compete in the 10-kilometre event on the sidelines of the Hong Kong Marathon, which has a record 72,000 participants in different categories this year.
The great-great-grandfather, who lives in Ilford, said he has "mixed feelings" about retirement.
"I fear that when I stop running, people will no longer love me. At the moment, everyone loves me... I hope nobody will forget or ignore me.
"When you become old, you become like a child and you want the attention," he said, comparing retirement to a "divorce" from a happy marriage.
Singh, who weighs just 52 kilograms (115 pounds), says he does not suffer any illnesses but admitted that "racing is getting tough" for him at his age.
"I feel that I must retire on a high," he said.
"I will not stop running, but will do it for my personal health."
Singh was inspired to take up marathons after he saw television coverage of one 12 years ago, not long after the death of his wife and a son and at a time when he said he needed a new focus in life.
Although widely regarded as the world's oldest marathon runner, Guinness World Records has not certified him as such since Singh cannot prove his birthdate. He has said there were no birth certificates when he was born.
But Singh has won widespread accolades.
He was a torchbearer for the 2004 Athens games and last year's London Olympics, and appeared in advertisement for a major sports brand several years ago alongside the likes of David Beckham and Muhammad Ali.
His trainer Harmander Singh said the centenarian will keep up his routine of running 16 kilometres every day even after retirement. The trainer said he was "intrigued and impressed" by the runner after coaching him for 13 years.
"He has a very positive attitude. If I say, 'Let's do 10 kilometres today', he will say 'Why not we do 20 kilometres?'" the trainer said, linking the spirit to his name "Fauja" which means soldier.