  Metal-poor globular clusters (GCs) can provide a probe of the earliest epoch
of star formation in the Universe, being the oldest stellar systems observable.
In addition, young and intermediate-age low-metallicity GCs are present in
external galaxies. Nevertheless, inferring their evolutionary status by using
integrated properties may suffer from large \emph{intrinsic} uncertainty caused
by the discrete nature of stars in stellar systems, especially in the case of
faint objects. In this paper, we evaluate the \emph{intrinsic} uncertainty (due
to statistical effects) affecting the integrated colours and mass--to--light
ratios as a function of the cluster integrated visual magnitude ($M_V^{tot}$),
which represents a quantity directly measured. Our approach is based on Monte
Carlo techniques for randomly generating stars distributed according to the
cluster's mass function. Integrated colours and mass--to--light ratios in
different photometric bands are checked to be in good agreement with the
observational values of low-metallicity Galactic clusters. We present
integrated colours and mass--to--light ratios as a function of age for
different assumptions on the cluster total $V$ magnitude. We find that the
emph{intrinsic} uncertainty cannot be neglected. In particular, in models with
$M_V^{tot}=-4$ the broad-band colours show an \emph{intrinsic} uncertainty so
high as to prevent precise age evaluation of the cluster. Finally, the present
predictions are compared with recent results available in the literature,
showing in some cases non-negligible differences.
