Randy's age in 'A Christmas Story' is not explicitly stated as a specific number in the movie, but from the way he behaves, interacts with his family, and his general appearance, he gives the impression of being around 8 or 9 years old. He's young enough to be excited about Christmas in a very child - like way, yet old enough to have his own little personality quirks that are different from a much younger child. His relationship with his older brother also gives some clues about his age. The older brother often seems to be more worldly - wise and Randy looks up to him, which is typical of an 8 - year - old with an older sibling.
One Christmas, Randy was turning ten. He was so excited because he thought that at this age, he was finally old enough to help his dad set up the Christmas lights outside. He climbed the ladder carefully, passing the bulbs to his father, and it became a special memory of that Christmas related to his age.
Well, if Randy was five, his Christmas story could be about believing in Santa Claus with all his heart. He left out cookies and milk for Santa and in the morning, he was overjoyed to see the presents under the tree. His age made this simple act of believing a pure and wonderful part of Christmas.