Yeah I started programming at age 12 myself back in the early 80's, but the basic language I used did not include the complxities of 3d.
This language is easy to learn, and maybe he won't have any problems at age 11.
However, unless he has a programming bug, I doubt he will stick with it.
Something less technical that offers faster results may be a better way to start for some people.
It doesn't hurt to try
FPSC, and then move into the realms of programming with DBPro when he wants to.
Maybe that will be right away, and thats okay.
I got both FPSC and DarkBASIC Professional because they are both awesome and very affordable.
It depends on the games he wants to build I guess, but FPSC is the way to develop a 3D game fast and easy for any age or experience level.
After all, he did say...
"Do you have any other suggestions?"
Post Script
FPS Creator was written using DarkBASIC Professional, and the source code for the engine is available from TGC.
So, if he does end up moving into DBPro, then he can even modify FPSC itself, and not just the games it creates.
I think that getting both products would be the best bet, and cover all your bases.
That way, he can get starting making his own custom 3D games right away with the ability to build on that as his skills develop.