  We use the Binary Population and Spectral Synthesis (BPASS) models to test
the recent suggestion that red supergiants can provide an accurate age estimate
of a co-eval stellar population that is unaffected by interacting binary stars.
Ages are estimated by using both the minimum luminosity red supergiant and the
mean luminosity of red supergiants in a cluster. We test these methods on a
number of observed star clusters and find our results in agreement with
previous estimates. Importantly we find the difference between the ages derived
from stellar population models with and without a realistic population of
interacting binary stars is only a few 100,000 years at most. We find that the
mean luminosity of red supergiants in a cluster is the best method to determine
the age of a cluster because it is based o the entire red supergiant population
rather than using only the least luminous red supergiant.
