Which exam is it? The OLSAT? Or a different test?

My understanding is that if it is for Intellectual assessment (IQ) then between the ages of 7 and 9 are optimal.

That said, my HG child did not pass the OLSAT, which he took in 2nd grade. Also, if it is the OLSAT, I believe you are allowed to prep for it. You are not allowed to prep for an Intellectual Ability (IQ) test, but from what I've heard prepping doesn't work for IQ tests anyway.