After middle age, further aging is associated with lower levels of many cognitive abilities, some of which could influence import economic decisions. Our prior research (Choi et al., 2014) shows a substantial negative relationship between age and the consistency of choices with economic rationality (decisionmaking quality). This paper investigates the sources of that negative correlation using panel data on more than 4,000 members of a panel study in the Netherlands. The analysis finds no evidence that the correlation between age and rationality is, in fact, a just a cohort, not an age effect. Similarly, there is little evidence that the correlation is due to other forms of cognitive or health declines. Rather, the findings indicate that age has an independent and negative effect on economic rationality.