What is the official age of Jim Henson's "Big Bird"?

Big Bird, a larger-than-human puppet, one of the creatures known as Muppets, created by puppeteer Jim Henson for the American children’s television program Sesame Street. Big Bird is a six-year-old walking, talking yellow bird with long orange legs, standing 8 feet 2 inches (2.49 meters) tall, that loves to read, sing, roller skate, ice skate, dance, write poetry, draw, even, ride a unicycle and resides in a nest at 123 1/2 Sesame Street. A running character on the TV program, Big Bird debuted in 1969.

Even though Big Bird debuted in 1969, Big Bird's age has been frozen at a particular point. In the film "Follow That Bird" (1985) he's 6 years old and still 6 years old in the 1989 special Sesame Street: 20 & Still Counting. Big Bird celebrated his 6th birthday, yet again, in the 1991 PBS pledge drive special Big Bird's Birthday or Let Me Eat Cake.