  A new equation for the density contrast is derived in the framework of
reexamined Newtonian cosmology taken into account adiabatic matter creation in
the universe.
  The age of the universe and the reach of the non linear regime of the density
contrast are usually treated separately in the literature and this may lead to
controversial conclusions regarding the most adequate scenario to describe the
universe.
  We relate the age of the universe and the growing mode of the density
contrast by introducing a variable $\xi$ that relates both of them, thus both
aspects are treated simultaneously. We apply this procedure to the Friedmann
type model where the source of particle production is given by $\Psi = 3 n
\beta H$.
