  The ages of young star clusters are fundamental clocks to constrain the
formation and evolution of pre-main-sequence stars and their protoplanetary
disks and exoplanets. However, dating methods for very young clusters often
disagree, casting doubts on the accuracy of the derived ages. We propose a new
method to derive the kinematic age of star clusters based on the evaporation
ages of their stars. The method is validated and calibrated using hundreds of
clusters identified in a supernova-driven simulation of the interstellar medium
forming stars for approximately 40 Myr within a 250 pc region. We demonstrate
that the clusters' evaporation-age uncertainty can be as small as about 10% for
clusters with a large enough number of evaporated stars and small but realistic
observational errors. We have obtained evaporation ages for a pilot sample of
10 clusters, finding a good agreement with their published isochronal ages. The
evaporation ages will provide important constraints for modeling the
pre-main-sequence evolution of low-mass stars, as well as to investigate the
star-formation and gas-evaporation history of young clusters. These ages can be
more accurate than isochronal ages for very young clusters, for which
observations and models are more uncertain.
