How old was Alex the parrot, the subject of an experiment by Irene Pepperberg, when it died?

Alex (May 1976 – 6 September 2007) was a grey parrot and the subject of a thirty-year experiment by animal psychologist Irene Pepperberg, initially at the University of Arizona and later at Harvard University and Brandeis University. When Alex was about one year old, Pepperberg bought him at a pet shop. The name Alex was an acronym for avian language experiment or avian learning experiment.

Before Pepperberg's work with Alex, it was widely believed in the scientific community that a large primate brain was needed to handle complex problems related to language and understanding; birds were not considered to be intelligent, as their only common use of communication was mimicking and repeating sounds to interact with each other. However, Alex's accomplishments supported the idea that birds may be able to reason on a basic level and use words creatively. Pepperberg wrote that Alex's intelligence was on a level similar to dolphins and great apes. She also reported that Alex seemed to show the intelligence of a five-year-old human, in some respects, and he had not even reached his full potential by the time he died. She believed that the bird possessed the emotional level of a two-year-old human at the time of his death.