youre ready when you start, and the sooner you start the better.
no matter how long you leave it, how much you develop your art and writing before you get started, your first comic will always be your worst. that is a guarantee. i say this to like every beginner bc its good, theres this quote from spike trotman that goes: "every person has 200 terrible comic pages inside of them, and the only way out is through." so just get started. quality be damned.
this is also the reason you should start small - start with something ten pages, then twenty, build it up - it builds your confidence and lets you know that you can finish things, and keeps things low commitment so youre more likely to finish. if you start off with a three year epic with no forseeable ending, youre bound to grow to hate it bc youll develop so much in even just a year, and youll want to move on to new styles, stories, and themes. staying short give you the freedom to move and develop with your practice.
i recommend listening to the episode of podcast dirty old ladies titled 'whats your excuse?' its all about people in your situation, hesitating to start, and its a really helpful and inspiring discussion.