I found a few publicly accessible biographies of Judit Polgár, including details of her early life. According to the biography on her website, she was 9 when she first won an international chess tournament. According to this SuccessStory article, she began participating in tournaments at the age of 6. According to this article from “All That’s Interesting”, she was able to beat her father by the age of 5.
But how old was she when she learned how to play?