There isn’t a requirement; you can compete whenever you want to. For a ladder competition I would suggest knowing all or most of the tricks on the list, however. Freestyles I usually consider someone who has at least expanded upon the base tricks to make their own combos, and a general sense of roping things together, ready for a freestyle based division. No matter what level you are, you won’t be disallowed to compete, you just might not make it very far, or make it past preliminary rounds. Key is to have fun.
These may or may not be the ones that your local contests will use. Most websites for your local contests will have a link or dedicated page showing the tricks they use in their Ladder and/or Pick-Your-Trick divisions.
For example, here is the division page for one of the contests in my area.