It's very very easy to make someone look younger in PS and there are heaps of tutorials on the web.
To make someone look older it's a lot more work. Here's a tute I found, I haven't actually tried it, and I think you have to be subscribed to access it. http://www.computerarts.co.uk/tutorials/premium_content/2d__and__photoshop/ageing_in_photoshop
(if the link doesn't work, just search for "ageing" in the tute part of the site)