Tamae Watanabe reached the 8,850 metre (29,035 feet) summit with a Japanese partner and three Nepali Sherpa guides on Saturday morning, said Ang Tshering Sherpa, who runs the Asian Trekking company, which provided logistics to the team.
"Watanabe and other climbers are in good physical condition. They are descending to their last camp which is located at an altitude of 8,300 metres (27,230 feet)," he said.
Watanabe, who first became the oldest woman to climb the mountain in 2002 at the age of 63, bettered her own record and set a new climbing feat, Sherpa said. She scaled the peak from the Tibetan side of the mountain.
Mount Everest straddles the Nepal-Tibet border. It has been scaled by 3,700 people since New Zealander Sir Edmund Hillary and Tenzing Norgay Sherpa first climbed it in 1953.
The list of climbers includes a blind person, a man with an artificial limb, a 13-year-old American boy and a 76-year-old Nepali man.
About 400 climbers are at camps on both sides of the mountain waiting for improved weather to make their summit attempts. Nepali tourism ministry officials said dozens of mountaineers had also climbed from the Nepali side of the mountain.