  The age of globular clusters inferred from observations depends sensitively
on assumptions such as the initial helium abundance and the mass loss rate. A
high helium abundance (e.g., $Y\approx$0.28), as well as an inclusion of helium
diffusion and oxygen-enhancement in stellar models, can lower the current age
estimate for metal-poor globular clusters from 14$\pm 1.5$ Gyr to about 11$\pm
1$ Gyr, significantly relaxing the constraints on the Hubble constant, allowing
values as high as 60km/sec/Mpc for a universe with the critical density and
90km/sec/Mpc for a baryon-only universe. The uncertainties of a high helium
abundance and an instability strip induced mass loss near the turn-off in
globular clusters are discussed. Ages lower than 10 Gyr are not possible even
with the operation of both of these mechanisms unless the initial helium
abundance in globular clusters is $>0.28$, which can hardly be accomodated by
indirect inferences of helium abundances in globular clusters.
