But Haizi started showing interest in courtship this spring, resulting in a blind date with a male panda suitor and - four months later - twin cubs that have made her the world's oldest panda mom, China's Giant Panda Conservation and Research Center announced today.
A 23-year-old giant panda is equivalent in age to an 80- year-old human.
According to the center, Haizi gave birth to a 175-gram (6 ounces) female and a 123.1-gram male on July 30 at southwest Sichuan province's Wolong National Nature Reserve, where 21 panda cubs have been born this year.
In Chinese culture, a set of boy-girl twins are called "dragon-phoenix babies."
"Generally, the maximum breeding age for giant pandas is 20 years old, and pandas older than that are not encouraged to participate in breeding," Li Desheng, a giant panda expert at the breeding center, said in a statement.
"But Haizi's success demonstrates the advanced degree of care offered at our center - it is a breakthrough in panda breeding.