  Despite the huge amount of photometric and spectroscopic efforts targetting
the Galactic bulge over the past few years, its age distribution remains
controversial owing to both the complexity of determining the age of individual
stars and the difficult observing conditions. Taking advantage of the recent
release of very deep, proper-motion-cleaned colour--magnitude diagrams (CMDs)
of four low reddening windows obtained with the Hubble Space Telescope (HST),
we used the CMD-fitting technique to calculate the star formation history (SFH)
of the bulge at -2deg > b > -4deg along the minor axis. We find that over 80
percent of the stars formed before 8 Gyr ago, but that a significant fraction
of the super-solar metallicity stars are younger than this age. Considering
only the stars that are within reach of the current generation of spectrographs
(i.e. V < 21), we find that 10 percent of the bulge stars are younger than 5
Gyr, while this fraction rises to 20-25 percent in the metal-rich peak. The
age-metallicity relation is well parametrized by a linear fit implying an
enrichment rate of dZ/dt ~ 0.005 Gyr$^{-1}$. Our metallicity distribution
function accurately reproduces that observed by several spectroscopic surveys
of Baade's window, with the bulk of stars having metal-content in the range
[Fe/H] ~ -0.7 to ~0.6, along with a sparse tail to much lower metallicities.
