One of the best computer art sites around is Worth1000. It has forums on using Photoshop, extensive galleries, and runs contests, some of which are for money (people wanting graphic designs, etc., will put up $50-100+ for something that meets their needs). It also has a superb tutorial section. A recent contribution to it was by "Grumplebits," explaining the steps in aging someone's face, using for an example the actress Katie Holmes, the future (?) / present(?) / former(?) Mrs. Tom Cruise. (I'm really not up on the latest Hollywood buzz.)
See, that's where the title comes from. One of Cruise's most famous roles was in Top Gun, and "Grumplebits" could also be considered a "Top Gun" of the . . . ah, forget it. Just go look.
I used a combination of the Stamp tool and Brush tool. I wish I could explain my technique at this point in a more clinical manner but mostly I relied on my artistic instincts. I emphasized the wrinkles around the eyes by widening and deepening the lines slightly and increasing the contrast by darkening the recesses and lightening the edges. Also, I extended wrinkles to the cheekbone areas. I then applied the same technique to the wrinkles around the mouth and to the forehead.