In Chapter 7 of "The Great Gatsby", what was so significant about Nick's 30th birthday?

There are many things that Nick says in the novel that seem to be for no reason but, at the same time, have great significance – this happens to be one of them.  Chapter 7 brings about a small get-together at the Biltmore Hotel including Tom, Daisy, Nick, Jordan, and Gatsby.  During this party, Gatsby and Tom get into a huge argument in which Tom reveals many of Gatsby’s shady secrets to Daisy, Jordan, and Nick.  Nick realizes after the entire fight is over that this was his 30th birthday.  The major significance is that Nick is so involved in the lives of the people around him that he does not even recognize such a major milestone in his own life.  Throughout the novel it is evident that Nick does not count himself as important as he does his relationship with the other characters and trying to be involved in the lives of those characters.  It is Nick’s statement about remembering his birthday that allows the reader to be aware of this.