The present study investigates the commonly found age-conservatism relationship by combining insights from studies on the development of personality and motivated social cognition with findings on the relationships between these factors and conservative beliefs. Based on data collected in Belgium (N=2,373) and Poland (N=939), we found the expected linear effect of age on indicators of social-cultural conservatism in Belgium and Poland and the absence of such effects for indicators of economic-hierarchical conservatism. We further demonstrated that these effects of age on indicators of cultural conservatism in both countries were (in part) mediated through the personality factor Openness to Experience and the motivated cognition variable Need for Closure. The consistency of these findings in two countries with a very dissimilar sociopolitical history attests to the importance of the developmental perspective for the study of the relationship between age and conservatism.