  Surface differential rotation (SDR) plays a key role in dynamo models. SDR
estimates are therefore essential for constraining theoretical models. We
measure a lower limit to SDR in a sample of solar-like stars belonging to young
associations with the aim of investigating how SDR depends on global stellar
parameters in the age range (4-95 Myr). The rotation period of a solar-like
star can be recovered by analyzing the flux modulation caused by dark spots and
stellar rotation. The SDR and the latitude migration of dark-spots induce a
modulation of the detected rotation period. We employ long-term photometry to
measure the amplitude of such a modulation and to compute the quantity
DeltaOmega_phot =2p/P_min -2pi/P_max that is a lower limit to SDR. We find that
DeltaOmega_phot increases with the stellar effective temperature and with the
global convective turn-over time-scale tau_c. We find that DeltaOmega_phot is
proportional to Teff^2.18pm 0.65 in stars recently settled on the ZAMS. This
power law is less steep than those found by previous authors, but closest to
recent theoretical models. We find that DeltaOmega_phot steeply increases
between 4 and 30 Myr and that itis almost constant between 30 and 95 Myr in a 1
M_sun star. We find also that the relative shear increases with the Rossby
number Ro. Although our results are qualitatively in agreement with
hydrodynamical mean-field models, our measurements are systematically higher
than the values predicted by these models. The discrepancy between
DeltaOmega_phot measurements and theoretical models is particularly large in
stars with periods between 0.7 and 2 d. Such a discrepancy, together with the
anomalous SDR measured by other authors for HD 171488 (rotating in 1.31 d),
suggests that the rotation period could influence SDR more than predicted by
the models.
