  (Abridged) We present a study of the disk population in L1688, the densest
and youngest region in Ophiuchus, and we compare it with other nearby regions
of different age, namely Lupus, Chamaeleon I, Corona Australis, Taurus and
Upper Scorpius. We select our L1688 sample using a combination of criteria
(ALMA data, Gaia, optical/near-IR spectroscopy) and determine stellar and disk
properties, specifically stellar mass (Mstar), average population age, mass
accretion rate (Macc) and disk dust mass (Mdust). a) In L1688 the relations
between Macc and Mstar, Mdust and Mstar, and Macc and Mdust have a roughly
linear trend with slopes 1.8-1.9 for the first two relations and ~1 for the
third, similarly to what found in the other regions. b) When ordered according
to the characteristic age of each region, Macc decreases as 1/t, when corrected
for the different stellar mass content; Mdust follows roughly the same trend
between 0.5 and 5 Myr, but has an increase of a factor ~3 at ages of 2-3 Myr.
We suggest that this could result from an earlier planet formation, followed by
collisional fragmentation that temporarily replenishes the millimeter-size
grain population. c) The dispersion of Macc and Mdust around the best-fitting
relation with Mstar, as well as that of Macc versus Mdust are large: we find
that the dispersions have continuous distributions with a log-normal shape and
similar width (~0.8 dex). The amount of dust observed at ~1 Myr does not appear
to be sufficient to assemble the majority of planetary systems, which suggests
an earlier planetary cores formation. The dust mass traces to a large extent
the disk gas mass evolution. Two properties remain puzzling: the steep
dependence of Macc and Mdust on Mstar and the cause of the large dispersion in
the three relations analyzed in this paper, in particular the one of the Macc
versus Mdust relation.
