A loyal Marginal Revolution reader asks about the relation between age and productivity.

There is a conventional wisdom to the effect that geniuses peak early, and are spent by the age of 30. This seems to originate from the retrospective glory accorded to some poets who died young, and to the physicist Paul Dirac's statements to that effect. There are several reasons this belief might be popular, not least because it reassures non-geniuses that they do not have so much to envy. But there is less reason to suppose that it is true.

It appears to me that productivity rises steadily with age, at least well into the forties, in any given field. However, the fields which permit greatest productivity are the newest. This is largely because, in a new field, less of the easy work has been done; in addition, the steady rise in societal productivity is largely caused by the invention of new, intrinsically more productive ways of working.

It is very difficult for a top producer to leave his field; thus breakthroughs visible to the nonspecialist tend to be made by those who have not yet specialized. This accounts for the continued perception that genius is for the young.

[Mr. Cowen answers a different question, here.]