  Massive halos of hot plasma exist around some, but not all elliptical
galaxies. There is evidence that this is related to the age of the galaxy. In
this paper new X-ray observations are presented for three early-type galaxies
that show evidence of youth, in order to investigate their X-ray components and
properties. NGC 5363 and NGC 2865 were found to have X-ray emission dominated
by purely discrete stellar sources. Limits are set on the mass distribution in
one of the galaxies observed with XMM-Newton, NGC 4382, which contains
significant hot gas. We detect the X-ray emission in NGC 4382 out to 4r$_e$.
The mass-to-light ratio is consistent with a stellar origin in the inner
regions but rises steadily to values indicative of some dark matter by 4r$_e$.
These results are set in context with other data drawn from the literature, for
galaxies with ages estimated from dynamical or spectroscopic indicators. Ages
obtained from optical spectroscopy represent central luminosity weighted
stellar ages. We examine the X-ray evolution with age, normalised by B and K
band luminosities. Low values of Log(L$_X$/L$_B$) and Log(L$_X$/L$_K$) are
found for all galaxies with ages between 1 and 4 Gyrs. Luminous X-ray emission
only appears in older galaxies. This suggests that the interstellar medium is
removed and then it takes several gigayears for hot gas halos to build up,
following a merger. A possible mechanism for gas expulsion might be associated
with feedback from an active nucleus triggered during a merger.
