  We use evolutionary calculations presented in a recent paper (Cassisi et al.
1998) to predict B,V,I magnitudes for stars in galactic globulars. The effect
of the adopted mixing length on stellar magnitudes and colors is discussed,
showing that the uncertainty on such a theoretical parameter prevents the use
of MS stars as bona fide theoretical standard candles. However, comparison with
Hipparcos data for field subdwarfs discloses a substantial agreement between
theory and observation. Present predictions concerning the magnitude of TO and
of HB stars are compared with similar results appeared in the recent
literature. We present and discuss a theoretical calibration of the difference
in magnitude between HB and TO as evaluated with or without element
sedimentation. Finally we use theoretical HB magnitudes to best fit the CM
diagram of M68 and M5, taken as representative of metal poor and intermediate
metallicity galactic globulars, deriving an age of 11$\pm$1.0 Gyr and
10$\pm$1.0 Gyr, respectively, for the adopted chemical compositions, plus an
additional uncertainty of $\pm$1.4 Gyr if the uncertainty on the chemical
composition is taken into account. This result is discussed on the basis of
current evaluations concerning cluster ages and distance moduli.
