I've been wandering about in raven country -- Montana, mostly -- for the past week, and the frequent sight of those strangely intelligent birds inevitably put me in mind of Bernd Heinrich's book on the subject, Mind of the Raven.
One of Heinrich's observations is that young ravens are endlessly curious and will investigate any unfamiliar obect placed in their territory. Sometimes this involves placing themselves in danger but they do it anyway. In this way, they acquire a stock of experience and information that will stand them in good stead for the rest of their lives.
Sometime around the time they reach sexual maturity, however, the behavior of ravens changes. They lose the curiosity. They distrust the new. Place something novel in their environment -- a whirligig, say -- and an old raven will eye it with suspicion and then fly far away.
The analogy with human beings is, I trust, obvious. This is why scientists usually make their great discoveries while young. This is why there are so many jokes about Gramps asking his ten-year-old for computer advice.
This is why some writers cease to be interesting after a certain age.
People have logical powers denied to even ravens, however. I think here of Tom Purdom, who sold his first two stories in 1957 but whose stories in the past decade are far superior to his earlier work and to most of what's published currently as SF to boot. If a writer can keep his or her curiosity alive,
maintain an interest in novelty for its own sake, and refrain from deciding she's (or he's) got enough knowledge to last, it's possible to go on and on.
But somewhere along the line, the writer has to consciously choose: young raven or old raven?