Time
John Scalzi made a post lately where he talked about the speed of publishing. Or, to be more accurate, the lack thereof. Someone asked him why new novelists always seem to be in their thirties, instead of twenties like musicians and actors, and he decided to give a nice long answer which is very illumating for people not well-versed in the world of publishing.
Part of his answer, of course, is that writing a novel takes time, and that usually an author’s first novel (and maybe their second, third, or more) is really not very good. Like any other art it takes practice. As he points out, in other crafts no one expects you to sit down and whip out a masterpiece on your first try. A new novelist’s debut novel is very rarely their first.
The rest of the answer has to do with the timeframes involved in publishing. Which are much longer than the average person suspects.
To start with, an aspiring novelist should find an agent to represent them. (Very important. The reasons why would be a whole ‘nother post.) This means sending out query letters, waiting for responses, and then sending out more. Usually if an agent is interested they’ll request sample pages. Then you wait to hear if they liked them. If they did, they’ll request the full manuscript, which can take months for them to read and respond to. Some people get lucky, of course, but for most the process takes at least several long months.
Once you have an agent they start sending your book to the publishing houses. And if you thought agents took a long time to get back to you, editors can be even worse. Though, once again, some people do get lucky.
So now an editor’s accepted your manuscript, and you’re going to be published. This, yet again, takes time. Between editing, copy editing, production, and release schedules, a book is usually published one to two years after it’s accepted.
After all of this, it’s not surprising that debut novelists in their early twenties are the exception instead of the rule.