  We analyze the non-standard mixing history of the solar twins HIP 55459, HIP
79672, HIP 56948, HIP 73815, and HIP 100963, to determine as precisely as
possible their mass and age. We computed a grid of evolutionary models with
non-standard mixing at several metallicities with the Toulouse-Geneva code for
a range of stellar masses assuming an error bar of +-50K in Teff. We choose the
evolutionary model that reproduces accurately the observed low lithium
abundances observed in the solar twins. Our best-fit model for each solar twin
provides a mass and age solution constrained by their Li content and Teff
determination. HIP 56948 is the most likely solar-twin candidate at the present
time and our analysis infers a mass of 0.994 +- 0.004 Msun and an age of 4.71
+-1.39 Gyr. Non-standard mixing is required to explain the low Li abundances
observed in solar twins. Li depletion due to additional mixing in solar twins
is strongly mass dependent. An accurate lithium abundance measurement and
non-standard models provide more precise information about the age and mass
more robustly than determined by classical methods alone.
