Color–magnitude diagram of the open cluster M 67. The black filled circles represent our work sample, i.e., stars with lithium abundance measurements. Stars with photometry available from Yadav et al. (2008), but with no lithium abundances, are displayed as open circles. The continuous isochrone from TGEC models with extra mixing corresponds to an age of 3.87 Gyr. The dotted line is the isochrone of 3.60 Gyr calculated from standard models.