Thinking out loud:
It will all depend on how much his skills and needs grow. A tablet is a really good idea as it's portable but not quite as powerful as a laptop would be. A laptop is the most powerful but is not quite as portable as a tablet would be.
I would think he might like a graphics tablet like the ones from Wacom. What I would do is skirt the issue; see what he's doing with his work and try to get an idea on what he would like (if you wanted this to be a surprise, anyway).
In addition, I realize artists use Photoshop to a great extent but there's something to be said for a good drawing/painting program that concentrates on that aspect, like Autodesk's SketchBook Pro or Ambient Design's ArtRage 4. (The former is available on just about every platform; Windows, Mac & mobile platforms Android and iOS. The latter is similar with the exception that it's not available for Android but a version is coming.) These programs can save and work with Photoshop files (PSD format) in the desktop versions.
Some mobile apps, like Photoshop Touch can work with Photoshop CC/CS6 in the sense that you can start a project on Photoshop Touch and finish it in Photoshop CC/CS6. (This is all though Creative Cloud, which is free to join.) The mobile version of SketchBook Pro can also save as PSD to cloud services like DropBox. The caveat with PS Touch is what I tell anyone interested in a drawing program: PS Touch is first and foremost an image editor as its drawing tools are somewhat basic compared to, say, SketchBook Pro.
ON EDIT: Forgot to add: If you want to get him Photoshop CC for use at home, Adobe has the Photoshop Photography Program available again for a limited time. (Gotta hurry, though; it ends March 31, 2014. I'm sure it'll pop up again at some point after but you'll have to wait unless you want to fork over more cash per month just to use Photoshop.)