A key question is whether both parents work. If not, I'd consider keeping him out of school this year and spending a lot of interactive time with him. In this case, you wouldn't need to test him until he's a bit older.

If both work, I'd guess that finding a high-energy teacher who would enjoy the challenges he presents is more important than getting him into a G-T program.

This POV isn't strictly responsive to your question, but I hope it's useful as you consider your options.