Recently, Nyki Blatchley put up a post about the kind of characters he likes to write about, with a fair amount of attention for the age of his protagonists, and that got me thinking about my own patterns.
I think most of us fantasy writers who started out young began writing about teenagers, both because of the appeal of the coming-of-age story and due to some degree of wish fulfillment. That's not to say this is a "newbie choice" - there are deep themes, both mythic and personal, that these characters make possible. People never stop discovering who they are, I think, so reading about a character who is undergoing that same journey in a world with very different possibilities than ours has a powerful draw.
If those of us who started writing these characters when we were knee-high make any mistakes, it may be that we make our protagonists a little too young, because it seems plenty old to us. I wrote or rewrote one of my early novels about three times; throughout, Nelia changed from being 17 to being 19 to being 21, and each time, that seemed like a massive leap to me as a writer (along with the thought of, "What was I thinking? She's too young."). Now, looking back on all those ages (never you mind how far), 21 seems the most reasonable. I wouldn't want to make her much older for the storyline I'd developed, but on the other hand, she needs time for her warrior training and other background.
In any case, when I started writing older, more established characters, it was a revelation. Characters who are embedded in their society, who have a stake in their own identities and what they've built, present a whole different set of challenges. It was ideal for Butterfly's Poison, my intrigue novel, because the resources of the characters - and most particularly, what they had to lose - were key to the plot. In many ways, I think I generally prefer this kind of character. On a personal level, I never really had that teenaged identity crisis of, "Who am I?" - I always was very centered in my sense of self. So it's hard for me as a writer to get into the mindset of that flux, and there's a degree to which I think I subconsciously believe it's not actually possible. ;-)
I find a lot of fertile ground in the idea of someone who has lost everything, who has start to over and reinvent themselves at a point when they thought they had the world figured out.
I have gone back to the teenager and the young adult. Anaea in Scylla and Charybdis discovers herself even as she discovers the rest of the universe. (She is also profoundly a misfit: her "calling" in life doesn't even exist in what she initially thinks is the full sum of human existence.)
Obviously, there are older and younger characters than this. I am fascinated by immortality and its ramifications, so I often write about immortals, especially gods. I think my childhood obsession with Greek myths has something to do with this: I never get tired of the juxtaposition between divinity and human pettiness.
... which probably explains the entire existence of Who Wants To Be A Hero?
I do touch upon the "merely" old, though not as frequently. One of my favorite characters in Who Wants To Be A Hero? is a contestant who happens to be the grandmatriarch of a pseudo-Norse clan. Still, if I were to make some conscious choices, this is an age demographic I'd like to pay more attention to.
I'm also fascinated by what I think of as the "eerie child" - the youngster who is far more poised and mature than their years would suggest. Humans develop cultural filters as they mature, and most of these are important for survival (at least until you move), but children who haven't developed these filters yet can see things the rest of us can't. Verdant from Taming The Weald is one of my best examples of this. (Shameless plug ... you knew there had to be at least one.)
If there's one thing all this brings to mind, it's that life is not always a straight line. We've reached the end and we're just starting out in unexpected places.