Yes, I do mean that his age has been considered in determining the scores. And yes, it is acceptable to administer them all in one session. No, you cannot request a re-test of any part. Tests of this nature are not supposed to be re-administered within this short a time period. Typically, the re-test interval for cognitive (reasoning) tests is two years.
I would first find out whether these scores are based on the general norms or the gifted norms, as it may be that the perception of lower-than-expected performance is misplaced to begin with. If, after answering that question, you still feel that this is inconsistent with your experience with your son, your options for appealing any decisions based on this testing will depend on the school. SAGES-2, although a decent instrument in its own way, is really a screening instrument. There are other tests of cognitive ability that are both more comprehensive and more nuanced, such as the WPPSI-IV and DAS-II.
On another note, I assume that your son is also a recent arrival to the USA, which means that any assessment using USA norms is an approximation at best, as his educational and cultural experience is not exactly represented by that of the children who made up the norm groups.
