Magnetic stellar evolution model tracks of the CM Dra stars. Models are computed at the precise masses of the CM Dra stars with [ Fe / H ] = −0.1 dex and [α/Fe] = + 0.2 dex. Solid lines show the evolution of models with no magnetic field, for reference. Magnetic models with a “rotational dynamo” and dipole radial profile are shown as dashed lines while dotted lines are magnetic models computed with a constant-Λ radial profile with a “turbulent dynamo”. Horizontal shaded regions mark the observed radius with 1σ uncertainties. The vertical stripe denotes the age constraint determined in Sect. 4.