Sure. You can go and learn how to write something. You can learn about the subject you’re writing about. You can investigate. You can work on your craft.
And you can get stuck, and not know what happens next, and wait until you do.
And you can discover that showrunning a tv show you’ve written takes all of your time, and put the novel you’ve been writing to sleep knowing that you won’t be waking it up and carrying on with chapter four until about 20 months have passed.
There aren’t any rules. I wrote a first draft of a first chapter of The Graveyard Book when I was 24, in 1985, and wrote the book between 2004 and the end of 2007. I started Coraline in 1990ish, stopped when I moved to the US in 1992, and finished it in 2000.