  The Procyon AB binary system (orbital period 40.838 years, a newly-refined
determination), is near and bright enough that the component radii, effective
temperatures, and luminosities are very well determined, although more than one
possible solution to the masses has limited the claimed accuracy. Preliminary
mass determinations for each component are available from HST imaging,
supported by ground-based astrometry and an excellent Hipparcos parallax; we
use these for our preferred solution for the binary system. Other values for
the masses are also considered. We have employed the TYCHO stellar evolution
code to match the radius and luminosity of the F5 IV-V primary star to
determine the system's most likely age as 1.87 +/- 0.13 Gyr. Since prior
studies of Procyon A found its abundance indistinguishable from solar, the
solar composition of Asplund, Grevesse & Sauval (Z=0.014) is assumed for the HR
Diagram flitting. An unsuccessful attempt to fit using the older solar
abundance scale of Grevesse & Sauval (Z=0.019) is also reported. For Procyon B,
eleven new sequences for the cooling of non-DA white dwarfs have been
calculated, to investigate the dependence of the cooling age on (1) the mass,
(2) the core composition, (3) the helium layer mass, and (4) heavy-element
opacities in the helium envelope. Our calculations indicate a cooling age of
1.19+/-0.11 Gyr, which implies that the progenitor mass of Procyon B was
2.59(+0.44,-0.26) Msun. In a plot of initial vs final mass of white dwarfs in
astrometric binaries or star clusters (all with age determinations), the
Procyon B final mass lies several sigma below a straight line fit.
