Left: relation between the convection parameter α_conv and the age. To compare models, we expressed α_conv in units of the solar value, which, as mentioned in Sect. 3.1, mainly depends on the convection theory used in the model, i.e. α_{conv, ⊙ ,cgm} = 0.688 and α_{conv, ⊙ ,mlt} = 1.762. The regression line is α_conv/α_{conv, ⊙} ≃ 0.13 × A + 0.59 (A in Gyr.). Colour symbols are for case 7 models (symbols and colours are listed in Table 2), grey symbols for case 6, and open blue for other cases. Right: relation between the initial helium abundance and the mass of HD 52265, as inferred from model optimization. The regression line is Y₀ ≃ −0.58 × M/M_⊙ + 1.00. Open red stars illustrate the impact of the Y₀-M degeneracy (Table A.1).