Melody composition and age

A reader writes:

I suspect that with composers there's an age correlation with melodic skill as well, i.e. other things being equal, a 40-year-old composer won't be nearly as melodically fertile as a 20-year-old composer. (He may, of course, be far superior to a 20-year-old composer in structural skills or other creative areas.) Maybe the brain cells that determine melodic ability are among those, like short-term memory cells, that decrease in numbers with the passing of years. I've never seen any print discussion of this theory. One reason I cherish Wagner so much is that his melodic inspiration flowed as freely in his old age as it did during his youth.

Has anybody ever done an objective study of the ages at which songwriters peaked? Irving Berlin, for example, was 23 when he wrote "Alexander's Ragtime Band" and 51 when he wrote "White Christmas," which sounds quite late in life to write a massive hit song. That's a long, long time to stay on top of the game. Richard Rodgers' last mega-musical, "The Sound of Music," debuted when he was 57.

Steve Sailer's homepage and blog is iSteve.com