Finite-sample effects on the observed-to-mock age histogram ratio. Blue line shows the normalized ratio between the observed and mock age histograms for solar twins based on M_Ks, identical to that shown in Fig. 1. Blue shaded region indicates the statistical uncertainty on this ratio, estimated from 10⁵ Monte Carlo realizations assuming Poisson statistics for the observed age histogram. Gray shaded region represents the 1σ sampling variance expected from finite-sample statistics, estimated by repeatedly drawing random subsamples from the mock catalog with the same number of stars as in the observed sample and computing the corresponding subsample-to-mock ratios.