Conceptual innovators (think Brin & Page) do their best work in their 20s, while experimental innovators (Mark Twain) do it in their 50s or later. The former group has a big idea and executes against that vision, while the latter experiments, tinkers, and refines to come up with something great. The article examines writers and painters, but I'd like to see a study examining this theory in the context of business folks and technologists.