Fluid intelligence, working memory, and processing speed all peak around age 23, while crystallized intelligence (closely associated with verbal intelligence) peaks in the 20s and holds or increases somewhat across the lifespan, absent other pathology. Our capacity to use crystallized and fluid intelligence effectively increases over the lifespan (this is the Wisdom leg of Sternberg's Triarchic Theory of Intelligence, also known as Successful Intelligence).

You may find this series of graphs from the standardization data on the WJIII of interest:

http://www.iapsych.com/iapresreport7.pdf

ETA: I realize that something cannot both peak and increase somewhat afterward, but this was less clunky than a more accurate statement reflecting the end of the steep portion of the GC growth curve.

Last edited by aeh; 07/10/15 09:52 AM.
...pronounced like the long vowel and first letter of the alphabet...