My son has autism/asperger's, too and he'll be 9 next month.
We tried a gluten-free diet with him, but didn't see any change. And it's something you'd have to try for quite awhile. Most folks will tell you that you need at least three months gluten-free before discarding the diet as ineffective.
Right now, we're trying the Fiengold diet, but it's too early to tell if it's working! I see a little improvement, but we just started it on Friday so it's too soon to make a pronouncement.
My belief is, it doesn't hurt to try a diet and see what happens. If it doesn't work, you can always resume a normal diet.