Bruce Charlton writes:
Provoked by your red-shirting comments [see below]...
I am re-reading Ian Deary's marvellous, concentrated little book Intelligence: a very short introduction; and from Chapter 2 on ageing (summarizing work by Salthouse) it is very clear that g begins to decline pretty early on average - in the 30s.
At the same time the average educational experience of professionals is now becoming so lengthened that plenty of people are mot starting their real jobs until g is already declining. I
For instance, scientists are now not finishing their post-doctoral training (often 5-6 years) until their mid-thirties - when they become eligible to apply for assistant professorships and (at last) begin their independnt researchers - just as g has started to decline. (and it shows...)
This is insane. We must stop lengthening, and start shortening, the duration of front-end formal education.
Contrast - in the great era of Cambrdige University in the early 20th century, the students would go to college at 19 for three years, and if they graduated with a first might get a college fellowship or equivalent within a year or two - to begin their independent researches in their mid-twenties.
Newton's epochal 18 months came at age 22-23.
James D. Watson retired from scientific research at age 39 and went into research management for the second half of his life.