These questions are open and vague. One could write pages upon pages in response, and the questions would still not be fully answered. I imagine your son will answer perfectly precise questions much more swiftly—exactly what he does in math.
For open and vague questions, offer a word limit (e.g., between 400 and 600 words), and let your son respond at his own pace. The focus is on keeping his response within the word limit. This will let him practice writing at different levels of detail. Once he gets the hang of it, introduce a loose time limit; the idea is to allow him to become comfortable with working under a time limit. Once he does this comfortably, tighten the time limit for more practice.
I do not think the questions are too advanced for him; rather, I think his thinking is too advanced for the questions as they were intended.
