The Great Gatsy is the story of a romantic heroic figure who rises and falls. Gatbsy may be flawed, but unless he is seen as a hero, the novel's narrative structure doesn't really work. As already stated, Nick is similar to Fitzgerald himself. But if a female character were to tell the story of Gatsby, it's likely she could only have told the story from the perspective of a character who was in love with Gatsby. This would not allow her the kind of objectivity that Nick manages to have most of the time. As well, having Nick feel a kind of obsessive admiration for Gatsby at times mimics the notion of romantic love, but the fact that Nick is male and that both are heterosexual allows for a more complex layer of perspective. To have the narrator be a female in love would make her more or less one dimensional; but Nick can explore hsi love of Gatsby in a more chivalric way.
The novel is written from the male perspective because Nick Carraway is representative of Fitzgerald himself (at least one part of him). Nick's Midwestern background and his personal observations and reactions reflect Fitzgerald's in many ways. In numerous critical biographies of Fitzgerald, the point is made that the author was in many ways a divided personality. His Midwestern values conflicted with the wealthy, glamorous, and often irresponsible life he longed for in his youth and led for many years. In this respect, Nick Carraway and Jay Gatsby function as the conflicting parts of Fitzgerald's own character; they are his alter egos. In the novel, Nick finally arrives at strong moral judgments about the selfish and amoral forces that ultimately destroy Gatsby. He leaves the East and goes back home to the Midwest.
One of the fascinations of Fitzgerald's personality was that as he was engaging in the lifestyle that broke him financially and destroyed his health, a part of him was objectively observing and condemning his own behavior. It was only at the end of his life, after experiencing what he called his emotional "crack up," that he found some peace. He was working hard and very professionally to complete a new novel, The Last Tycoon, when he died of a heart attack in Hollywood at the age of 44. Based on his notes and the chapters he had already drafted, critics now say that it would have been a fine work.
I always thought that the reason why a male narrator would be picked over a female would be (although it's sterotypical) beacuse, from the veiwpoint of a woman, everything is drama, and gossip, and emotional. I am a girl, I know that this isn't entirely true, but to Fitzgerald, it may seem so, in his time women were not too promient, nor too intelligent, in schooling and what-not.