sartorias points to an essay by Justine Larbalestier on publishing too young.
I actually did sell my first professional story young–at 23–and it’s true that I knew a lot less about writing than I thought I did. Yet when I look back at that and other stories from my early twenties, I’m not, for the most part, embarrassed by what I see, though I think (know) my writing is much stronger now.
One thing I helped, I think, was being really, really picky about markets. I have some work from the same time as my first few sales that would have been embarrassing–but for the most part, no one published it. Not a foolproof plan, but the better the market, the lower the chance something will be accepted there that will embarrass one later. The flip side being that this means publishing more slowly–but I don’t know that an extra half dozen or dozen weaker stories published early on would have helped my career any.
Though then there are the stories one believes in even after every market you’re willing to submit to rejects them … but that’s a subject for another post.