I just read a fascinating article in the July Wired magazine about creative genius. The subject, an economist named David Galenson, has correlated age with perceived value in all sorts of creative fields, and has identified 2 curves. One, which he dubs "Concepualists", tend to peak early in their careers. For example, even though Picasso lived into his 90's, his most cited works in art history and other books were done before he was 30. Mark Rothko, (one of my favorites), did his most cited work the year he died, when he was 59. Galenson calls these guys "Experimentalists". He has done this correlation over painting, fiction, economists, music, and other fields. He believes that 2 distinct flavors of genius exist: one that manifests itself early, with bold, field-changing paradigm shifts (concepualist) and another, slower, accumulated genius (the experimentalist).
This instantly applies to other fields that he hasn't studied, like physics. I've often wondered why so many brilliant, earth shattering discoveries are made by young men Newton, Einstein, and Feynman were quite young when they produced their landmark works). However, if you look at someone like Stephen Hawking, he's still producing significant work. I think this is a great topic, one that resonates with observations I've made but never correlated myself. His book is named Old Masters and Young Geniuses: The Two Lifecycles of Artistic Creativity, and it's jumping to the top of my reading list with a bullet.