My read on it is perfectionism mixed with a lack of organizational skills for writing with perhaps a heavy dose of the forest-view sort of gifted mind.
On the perfectionism front, I know adults who want to write novels but never start because they don't know how to get it published. It's a sort of long-sighted short-sightedness. There are some common (possibly mythical) numbers like on average a writer gets their twelfth novel published first. 10 or 12 rewrites of screenply before it filmed. Pretty common number. And that's what professionals do.
For skills, perfectionism, big picture thinking (and for many career endeavours) the key skill is organizing thoughts into bite size executable pieces. Start first with unstructured brainstorming of ideas, points, counter points. Capture those, organize them, hone them down and writing the most clear piece first (not starting at word one and end-to-end one word after another.) I'd look into helping him find graphical tools for organizing thoughts like thought maps.
