  We reconsider the problem of the age of the stellar discs of late-type Low
Surface Brightness (LSB) galaxies by making use of a new IMF recently derived
from numerical fluid dynamical simulations (Padoan, Nordlund and Jones, 1997).
While a Miller-Scalo IMF cannot adequately describe the photometric properties
of LSBs, when we apply the new Padoan et al. (1997) IMF to a simple exponential
disc model with parameters appropriate to LSBs, we get excellent fits of the
colors and color gradients. We then conclude that: a) The star formation
history of LSB disc galaxies can be described by an initial burst of a few
times $10^7$ yr followed by a quiescent period with only sporadic star
formation; b) LSBs' discs are not young. The age of the LSB disc galaxies for
which colors have been measured are all larger than about 10 Gyr$.
