Age distributions for the thin-, hαmr, and hαmp thick-disc populations, from left to right panels, respectively. Top panels: age distributions from the APOKASC catalogue (red histogram) and with a relative error of less than 25% (grey dotted line). Bottom panels: age distributions from M21 (blue solid line) and from APOKASC (with a relative error less than 25%) for the subsample of stars in common (red solid line).