I’m going to punt here. If he were a student…yes. But he is living in his own place. For FAFSA purposes, how,can you count him as a member of YOUR household. He is not a member of your household. He lives someplace else.
ETA…and while tax filing status doesn’t detemine financial,aid status, if your son is NOT on your tax return as a dependent, I would think this would be a verification red flag.