world is one's oyster, the - Phrases/Idioms
The American Heritage® Dictionary of Idioms by Christine Ammer. Copyright © 2003, 1997 by The Christine Ammer 1992 Trust. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
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.”