Testing at 6 or even 8 is generally considered more reliable, but we had to have our DD tested earlier than that to get any traction with school. And it while it didn't solve a our problems it did instantly switch schools response from "crazy pushy parents" to "well if the psychologist says she's gifted and needs xyz.." We didn't magically get everything DD needs but we did get actual conversations... So testing younger than ideal was useful for us.