Nick's maturation in "The Great Gatsby" is most prominently exemplified by his views on the value of money. His feelings towards the subject of materialism and prosperity in general undergo a subtle transformation throughout the novel, and it is through this mental development that we see Nick step into the threshold of a sagacious adulthood.
We learn early on that Nick is in the bond business, and came to the East to pursue his career. He "bought a dozen volumes on banking and credit and investment securities, and they stood on my [Nick's] shelf in red and gold like new money from the mint, promising to unfold the shining secrets that only Midas and Morgan and Maecenas knew" (Fitzgerald 10). Nick is clearly attracted by the prospects of what money can do for a man in the 1920's, and is certainly intent on getting some. Although Nick is in his late-twenties at the beginning of the novel, his states, on page 10, that moving to West Egg made it feel as if "life was beginning over again with the summer".
He is, as all young men are apt to, excited by the prospect of an adventure in an unknown land, and looks forward to the opulence which this 'new life' will bring.
With this mindset, Nick enters the world of the wealthy, and it is far from what he'd expected. A visit to the well-to-do Buchanans left Nick "confused and a little disgusted" (24). A meeting with Tom's mistress and her friends causes Nick to be "simultaneously enchanted and repelled by the inexhaustible variety of life" (37). An appearance at one of Gatsby's parties gives Nick the feeling that the 'upper class' is every bit as prodigal and graceless as he had hope them not to be.