... 1) The MS lower envelopes for groups of stars with different metallicities turn out to be coincident. ... 4) The conformation of the kinematics of stars within narrow ranges ob b-y with the ages derived from isohrones reveals that, at Z < Z , the isohrone ages seem to be increasingly overestimated with growing b-y . ... At a given metallicity, they have a much narrower MS and the locus of their MS lower envelope seems to be brighter for the metal-rich group of stars. ...