  [Abridged] We present two deep surveys of circumstellar discs around
solar-type stars at different ages carried out at 350 micron with the CSO and
at 1.2 mm with the IRAM 30-m telescope. The aim of this study is to understand
the evolution timescale of circumstellar debris discs, and the physical
mechanisms responsible for such evolution around solar-type stars. In addition,
we perform a detailed characterisation of the detected debris discs.
Theoretically, the mass of the disc is expected to decrease with time. In order
to test this hypothesis, we performed the generalised Kendall's tau correlation
and three different two-sample tests. A characterisation of the detected debris
discs has been obtained by computing the collision and Poynting-Robertson
timescales and by modelling the spectral energy distribution. The Kendall's tau
correlation yields a probability of 76% that the mass of debris discs and their
age are correlated. Similarly, the three two-sample tests give a probability
between 70 and 83% that younger and older debris systems belong to different
parent populations in terms of dust mass. We detected submillimetre/millimetre
emission from six debris discs, enabling a detailed SED modelling. Our results
on the correlation and evolution of dust mass as a function of age are
conditioned by the sensitivity limit of our survey. Deeper millimetre
observations are needed to confirm the evolution of debris material around
solar-like stars. In the case of the detected discs, the comparison between
collision and Poynting-Robertson timescales supports the hypothesis that these
discs are collision dominated. All detected debris disc systems show the inner
part evacuated from small micron-sized grains.
