What is the significance of Nick turning thirty?

The significance of Nick turning thirty is that he now considers that his youth has passed and he is facing a lonely and unfulfilling future. Throughout the novel, Nick has been the narrator of the story; he has been more of an observer than an actor or character. He has been inspired by the passionate dream of Gatsby and in his admiration for Gatsby's determination and persistence he sees himself in a less favourable light. He realises that he does not have a dream of his own; he does not engage deeply in emotional relationships; and he does not have close friendships. Now, as he looks to his future, he contemplates a lonely and unexciting life; everything appears to be dulling and fading, everything is becoming "thin"--his hair, his friendships, his opportunities.