We investigate starspot distributions consistent with space-based photometry of F , G , and K stars in six stellar associations ranging in age from 10 Myr to 4 Gyr .
We show that a simple light curve statistic called the “ smoothed amplitude ” is proportional to stellar age as t ^ { -1 / 2 } , following a Skumanich-like spin-down relation .
We marginalize over the unknown stellar inclinations by forward modeling the ensemble of light curves for direct comparison with the Kepler , K2 and TESS photometry .
We sample the posterior distributions for spot coverage with Approximate Bayesian Computation .
We find typical spot coverages in the range 1-10 % which decrease with increasing stellar age .
The spot coverage is proportional to t ^ { n } where n = -0.37 \pm 0.16 , also statistically consistent with a Skumanich-like t ^ { -1 / 2 } decay of starspot coverage with age .
We apply two techniques to estimate the spot coverage of young exoplanet-hosting stars likely to be targeted for transmission spectroscopy with the James Webb Space Telescope , and estimate the bias in exoplanet radius measurements due to varying starspot coverage .