Period-age diagram. Panel a shows the predicted period-age distribution (darker tones indicate a higher expected number of LPVs on a linear scale, normalized to maximum). Symbols represent observed LPVs (green: SRVs; purple: Miras; white: unclassified) with the shape indicating their host cluster or literature source as indicated in the legend. The age uncertainties are marked by the error bars. The groups of galactic C-stars of Feast et al. (2006) are marked by crosses annotated with the group number. The solid and dotted line represent a linear best-fit to models and the best-fit by Grady et al. (2019), respectively. Period distributions at selected ages are compared in panels b and c and marked in panel a by the blue and red shaded areas (at log(τ/yr) ∼ 9.15 and ∼10.10, respectively). For clarity, the effect of the TP-AGB boosting is suppressed in panel a.