Earlier retirement, earlier memory decline.

In yet another example of "use it or loose it," Rohwedder and Willis show that the earlier people retire, the more quickly their memory and general cognitive abilities decline. They note two possible models for the cognitive decline: 1.) A "unengaged lifestyle hypothesis" that suggests that the life of a retiree may lack the cognitive stimulation of the former working environment unless deliberate offsetting actions are take. 2.) A “on-the-job” retirement effect, in which mental effort decline as the retirement age approaches (a 50-year-old worker in the United States who expects to work until 65 has a much greater incentive to continue investing in mental capacity than does a worker in Italy who expects to retire at 57.) Here is a summary graph (details are in the article) :

Cognition by Percent Not Working for Pay, 60–64 Year-Old Men and Women, Weighted