  Two frequency observations, mainly at 1.4 and 5 GHz from the VLA, have been
used to study spectral variations along the lobes of some nearby low luminosity
radio galaxies that constitute a representative sample selected from the B2
catalogue. The variations of the spectral index have been interpreted as being
due to synchrotron and inverse Compton losses and characteristic spectral ages
are deduced for the relativistic electrons. The radiative ages are in the range
of several 10^7 years. These ages correlate well with the source sizes. They
also appear to be consistent with dynamical ages determined from ram-pressure
arguments, if we make reasonable assumptions about the ambient gas density and
allow for very moderate deviations from the equipartition conditions. There
appears to be a significant difference between the radiative ages of sources in
our sample and those of more powerful 3CR radio sources. We briefly discuss the
possibility of re-acceleration processes and indicate some objects where these
may occur.
