Odds of Getting In
Just being a basic catering server is a no-brainer—literally. Big catering companies are used to an incredibly high turnover rate (people quitting vs. staying) so for the everyday functions, they'll hire almost anyone.
Actually running your own catering business is a whole other ballgame. If you have the drive, the know-how, and the funding, you can set up shop and start advertising ASAP. Basic services are still a fairly cheap enterprise, but setting up your own kitchen is expensive.
Thankfully, there are companies out there that'll let you rent equipment. Their business is catering to caterers, and as a beginner, you'll be incredibly happy to have them.