She is named # 21 because she is wild born. She is approxiamtely 22-25 years old and is currently on loan to the Xiamen Haicang Safari Park in China from the Bifengxia Panda Base, outside of Ya'an China.
While she was living at the Wolong Panda Base before the May 12, 2008 earthquake, she took part in the breeding program and has had quite a few cubs while living at the Wolong Panda Base. Long Hui, (male, Zoo Vienna, Austria), Lin Yang, (male, Fuzhou Panda Center, China) Gong Zhou (female, Bifengxia Panda Base, China) Lin Hui (female, Chiang Mai Zoo, Thailand).
Thanks to yingying816 of YouTube for providing these photos you can see videos of Panda #21 on their site.