While the strong anticorrelation between chromospheric activity and age has led to the common use of the CaII H and K emission index (R'HK=L_HK_/L_bol_) as an empirical age estimator for solar-type dwarfs, existing activity-age relations produce implausible ages at both high and low activity levels. We have compiled R'HK, data from the literature for young stellar clusters, richly populating for the first time the young end of the activity-age relation. Combining the cluster activity data with modern cluster age estimates and analyzing the color dependence of the chromospheric activity age index, we derive an improved activity-age calibration for F7-K2 dwarfs (0.5