I took my first SAT and ACT really young (didn't know about SET, but needed it for college courses). Does he have any older friends/cousins/classmates... taking it that day? For me, they put me in the same room as my senior classmate so that he could help me with finding the room again after breaks/finding the bathroom/registration... It was a pretty good solution, and I'd recommend it.
There wasn't a writing section when I took it, but they did allow me to read by the proctor during breaks and as a back-up if I hit my limit of testing. However, I was pretty excited by the whole experience and was able to work through all of the sections, though I didn't finish every section in the allotted time. You may want to explain that and go over filling out a scantron sheet before he takes the exam, if he decides to take it. Those were my biggest issues as a very young tester.
