[alexvr]

I did some research after asking this, and the studies' results seem to contradict each other. Apparently, our brains are largest at the age of 14, and we're smartest at about 15, especially in terms of new concept absorption. While that may be true, I once read that a fatty substance called myelin, which apparently facilitates rapid and efficient processing, is most ubiquitous in the brain in your early twenties, and a gradual decrease in this substance is probably responsible for mental decline. But a major longitudinal study on the topic found that mental abilities are largely constant from 20 to 60, and that through training, elderly brains can be significantly revitalized. I theorize that a major confounding factor is the tendency to retire around 60.

[tehwalrus]

it would be really cool to see some of the sources you found in your research... :)

[alexvr]

I learned a lot from the Seattle Longitudinal Study. This diagram basically sums up their findings: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1474018/figure/F... Also, they mentioned that if you correct for the loss in perceptual speed that comes with age, the drop is not as significant. I interpret this as, "If we give elderly people as much time as they need to take an IQ test, their performance will be relatively close to that of 20-somethings taking the same test under the same conditions." (I may be wrong, but that's what I would like to think.) I also found a study by UVA that is looking for participants, in case anyone is interested: http://faculty.virginia.edu/cogage/