An interesting post about the developing brain (and we are not just talking about the childhood period) points out that at least the white matter component of our brain does not fully develop until around the age of 40.
A longitudinal study that examined white matter over a lifetime found that white matter peaked at the ripe old age of 39. Interesting there was a correlation between maximum finger tapping speed and the measurement of myelin (white matter) they used – and they both in fact peaked at 39. Now finger tapping isn’t a higher cognitive function like inductive reasoning but if offers us some hints.
Additionally, this peak of white matter in middle age might partially accound for the peak in a host of higher cognitive functions that include inductive reasoning and verbal ability which peaks in our 40’s and 50’s.