  The mid-infrared (10-20 um) luminosity of elliptical galaxies is dominated by
the integrated emission from circumstellar dust in red giant stars. As a single
stellar population evolves, the rate of dusty mass loss from red giant stars
decreases with time, so the mid-infrared luminosity should also decline with
stellar age. To seek such a correlation, we have used archival ISO observations
to determine surface brightness profiles and central fluxes at 15 um in 17
early-type galaxies for which stellar ages have been determined from optical
spectral indices. The radial surface brightness distributions at 15 um
generally follow the stellar de Vaucouleurs profile as expected. We find that
the surface brightness ratio mu_{15um}/mu_{I-band} is systematically higher in
elliptical galaxies with ages < 5 Gyrs and in galaxies that exhibit evidence of
recent mergers. Within the accuracy of our observations, mu_{15um}/mu_{I-band}
shows no age dependence for ages > 5 Gyrs. The corresponding flux ratios
F_{15um}/F_{I-band} within apertures scaled to the effective radius (R_e/8) are
proportional to the mu_{15um}/mu_{I-band} ratios at larger galactic radii,
indicating that no 15 um emission is detected from central dust clouds visible
in optical images in some of our sample galaxies. Emission at 15 um is observed
in non-central massive clouds of dust and cold gas in NGC1316, an elliptical
galaxy that is thought to have had a recent merger. Recent {\it Spitzer Space
Telescope} data also indicate the presence of PAH emission at 8 um. Several
ellipticals have extended regions of 15 um emission that have no obvious
counterparts at other frequencies.
