Takao Arayama, age 70 years, 7 months and 13 days, was the oldest person ever to scale the mountain's 29,035-foot peak, according to Toshinori Koya, an official at Tokyo-based Adventure Guides, which planned the climb.
The Guinness World Records Web site says the record has been held by another Japanese, Yuichiro Miura, who reached the famed peak at the age of 70 years, 7 months and 10 days, on May 22, 2003.
Arayama, who climbed the mountain as part of a five-member team, reached the summit at 10:45 a.m. Nepal time Wednesday morning, Koya said.
He said team leader Kenji Kondo, 43, contacted the company via satellite phone several hours after reaching the peak.
Everest straddles the Nepal-China border. It wasn't immediately clear which side Arayama's team used to scale the mountain.
Arayama, a corporate management consultant from Kamakura, near Tokyo, has now safely descended to a camp lower down on the mountain and is in good health, Koya said.
Kate White, a spokeswoman for London-based Guinness World Records, said Wednesday, "We have not had any report of this record. If he (Arayama) is older, we would look forward to announcing a new Guinness World Record.
In order to do so, she said they would need his birth certificate, photographs, witness statements and a log book of his climb.