Age-mass-chemical-composition scatter plots of stars in our sample (R < 11 R_⊙ and including RC stars with M > 1.2 M_⊙, see main text for details). Black crosses indicate typical uncertainties on the relevant measured/inferred properties. Top panel: age vs. [Fe/H]. The colour represents [α/Fe]. Upper middle panel: age vs. [α/Fe]. Red dots denote α-rich stars that are considered outliers based on their mass or age (see Sect. 5.2 for the criterion used). Lower middle panel: stellar mass versus [Fe/H]. The mass of 11-Gyr-old RGB models of different metallicity is shown as a solid line. Bottom panel: [α/Fe] versus [Fe/H], where the age is represented by colour. Red dots identify age/mass outliers among the α-rich population. Top and lower middle panels: mass, chemical composition and inferred age for eclipsing binaries in the old-open cluster NGC 6791 (Brogaard et al. 2012), the old metal-rich subgiant HD 89345 (Van Eylen et al. 2018, [α/Fe] is not available for this object), and in well-studied metal-poor objects: RGB stars in the globular cluster M 4 (Kaluzny et al. 2013; Miglio et al. 2016) and the nearby subgiant ν Indi (Chaplin et al. 2020).