  Thanks to recent high resolution ALMA observations, there is an accumulating
evidence for presence of giant planets with masses from $\sim 0.01$ Jupiter
mass to a few Jupiter mass with separations up to $ 100$~AU in the annular
structures observed in young protoplanetary discs. We point out that these
observations set unique "live" constraints on the process of gas accretion onto
sub-Jovian planets that were not previously available. Accordingly, we use a
population synthesis approach in a new way: we build time-resolved models and
compare the properties of the synthetic planets with the ALMA data at the same
age. Applying the widely used gas accretion formulae leads to a deficit of
sub-Jovian planets and an over-abundance of a few Jupiter mass planets compared
to observations. We find that gas accretion rate onto planets needs to be
suppressed by about an order of magnitude to match the observed planet mass
function. This slower gas giant growth predicts that the planet mass should
correlate positively with the age of the protoplanetary disc, albeit with a
large scatter. This effect is not clearly present in the ALMA data but may be
confirmed in the near future with more observations.
