Everything is going well, as in I was younger then, and the world was my oyster. In this term the oyster is something from which to extract great profit (a pearl). It was probably invented by Shakespeare in The Merry Wives of Windsor (2:2): “Why then, the world's mine oyster, which I with sword will open.”
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.