An interesting post over at Marginal Revolution discusses, in part, whether younger scientists tend to be more innovative than older scientists, and if so, should this issue be considered in terms of implementing policy. I have found this issue fascinating ever since I read Greatness: Who Makes History and Why by Dean Simonton (a fantastic book, by the way). I recommend going over to the post and reading both the main article, as well as the comments (several of which are excellent). In particular, I agree with a comment by "Agnostic," who also cites Simonton:
The go-to source is Dean Simonton. See his *Creativity in Science* (lots of data). In sum, the more fluid intelligence is required to excel -- physics or math -- the younger the scientist tends to produce their greatest work. Where success is more based on crystallized intelligence (having a large store of facts to examine) -- medicine or history -- they flourish later.
And of course that'll vary within a field. More naturalist types of biologists like E.O. Wilson do their best work later in life. Physicist imperialists like Francis Crick will do their best stuff very early on.
Really, just look up your heroes and see when they did their best work -- if they were fluid intelligence types, you'll get pretty depressed. Einstein's "miracle year" of groundbreaking work was 1905 -- when he was 26 years old.
Intelligence research shows that fluid IQ starts to decline after 30, and really plummets in middle age. No time for dilly-dallying!
If I recall correctly, this breakdown tends to hold in other areas of achievement as well, when all else is equal. For example, in terms of literary achievement, poets tend to produce their most innovative, ground-breaking work at the youngest average age of any writers, while literary criticism is often writen at its best by older writers. Poetry is a visceral, instinctive form that is often at its best when it is deeply personal, and defies "accepted standards." Non-fiction, criticism, etc., on the other hand, generally depends on a well-developed knowledge of the field in question. Poetry is much more of a fuild intelligence endeavor, while theory and criticism is much more of a crystallized intelligence activity. You can probably make the same argument for songwriters as well; in most cases, the most innovative stuff comes early, the more polished (but conforming) stuff comes later.