Another affect of ageing is that the whites of the eyes become slightly darker as you get older, so we can knock off another few years by restoring some youthful brightness.
To do this, use the Polygon Lasso tool with the feather set to 2 pixels. Carefully select the white part of one eye. Holding down the Shift key will allow you to add other unconnected areas to your selection, so you can have all the white areas selected at once.
To increase the brightness you can use the Brightness/Contrast control found in the Image > Adjustments menu, but personally I prefer the more precise control of the Levels dialogue. You can also find this in the Image > Adjustments menu, or by using the keyboard shortcut Ctrl-L.
Moving the centre slider towards the left will increase the brightness of the selected area. Only a small adjustment should be necessary to restore the whiteness of the eyes. If you overdo it your subject will end up looking like a Goa'uld, which may be a great way to scare Stargate fans, but it won't do much for your reputation as a portrait photographer.
The secret of successful retouching is the cumulative effect of a number of small changes. While none of the techniques on their own will have much effect, the total is greater than the sum of its parts and the overall result is a pleasant, if slightly dishonest, portrait.