Why do you say "an old lady can climb a mountain faster than a monkey"?

This sentence comes from: eighteen eccentrics in Yunnan-"The old lady climbs mountains faster than monkeys". There are many mountains and deep valleys in Yunnan, and local women live in the mountains all the year round. They have been trying to do heavy manual work since childhood. They are used to climbing mountains and chopping wood, so they have strong bodies and feet. Many young people in the mainland often can't catch up with the local old ladies in walking and climbing mountains, and the old people in their seventies and eighties often climb mountains.