  We report on near IR ($J$ and $K$ bands) observations of two $8 \times 8
\~(arcmin)^{2}$ regions centered on the old open clusters Berkeley~17 and
Berkeley~18, for which only optical photometry (in $B$,$V$ and $I$ bands)
exists. $J$ and $K$ photometry allows us to obtain an independent estimate of
cluster metallicity by means of the relationship between the spectroscopic
metallicity and the Red Giant Branch (RGB) slope calibrated by Tiede et al
(1997). From the analysis of the colour magnitude diagram (CMD) and luminosity
function (LF), Berkeley~17 turns out to have a metal content
$[Fe/H]~\sim~-0.35$. It is $9~Gyr$ old, suffers from a reddening $E(B-V) = 0.58
mag$ and has an heliocentric distance of $2.5 kpc$. Berkeley~17 comes out to be
substantially younger than in previous work (age $\approx 13~Gyr$). On the
other hand Berkeley~18 is found to have solar metal abundance, and to be
younger than Berkeley~17, with an age of about $4~Gyr$. While we confirm
Kaluzny (1997) reddening estimate, we significantly revise the distance of the
cluster, which lies $4.5 kpc$ from the Sun. These results on two open clusters
believed to be between the oldest put constraints on the age and the evolution
of the Galactic Disc. The absence of clusters older than $8-9~Gyr$ suggests the
possibility that the Galaxy underwent a star formation minimum between 13 and
$10~Gyr$ ago.
