How old is Jim in "The Gift of the Magi"?

In The Gift of the Magi, we find out that Jim is twenty-two years old.  We learn Jim's age near the end of the story.  At the beginning of the story, we learn other information about Jim, such as how much money he makes per week and what his most prized possession is.  O. Henry leaves out Jim's precise age at this point in the story, only mentioning it later on when he enters the small apartment after work.  After stating Jim's age, O. Henry writes that despite his youth, he works hard.  Jim has to support his family, which consists of his wife, Della.  O. Henry continues to describe qualities of Jim, such as his appearance.  

The writer may have chosen to not mention Jim's exact age at the beginning of the story because he felt that it was unimportant to the plot.  His age is mentioned as more of an afterthought.