Performance of the XGBoost chemical age estimator for the unseen test data. Top panel: spectroscopic age vs. asteroseismic age (from Miglio et al. 2021), using our default model. The solid black line and the shaded areas delineate the median trend and 1σ quantiles. The dashed line delineates the identity line, while the grey dotted lines correspond to ±25% deviation. Bottom panel: residuals (spectroscopic – seismic age), showing that our model typically provides reliable ages (with systematic residuals within ∼0.5 Gyr for stars with ages ≤11 Gyr).