I got my start in programming around the same age using tools from Clickteam [1]: Klik & Play, The Games Factory, and eventually progressing to Multimedia Fusion (now Clickteam Fusion). These are all drag-and-drop tools, with graphical level editors, event loop editors, etc.
If he doesn't mind using a Windows machine for development (the actual outputs are cross-platform), I think it's a great place to start before moving on to programming languages.