In terms of age, I think I've covered about as wide a range as is possible, having written everything from picture books to early chapter books to middle grade novels to YA to one adult novel - and having been editor and lead writer for a magazine for retired people!
I tend to be more of a novel writer. In fact, some of my novels started out as short stories, and I just got carried away! I think some of my best writing is in the short story form, but novels come more naturally to me.