How old is he right now? Is he very ahead academically? If he is reading well or doing very well with math; I would consider getting achievement testing done and then submitting the results for consideration for the YS program.
Some testers calculate the prorrated FSIQ w/o the coding section and I am pretty sure that number would be over the magic 150.
I would consider giving him the WISC when he is 6. My dd did not do very well in the WPPSI, but she had a very irregular testing experience. The academic gap from her to her peers only increased with time so we retested with WISC when she was ~7. That and qualifying AT (achievement testing) got her accepted.
My younger one tests very close to the DYS requirements in the WPPSI (like your son in the 99.9%)but we won't retest her unless/until she is much more ahead academically OR if we had reason to suspect some LD (learning disability).
