As someone who was that sort of child, and to a degree still is, I'm going to do the whole "devil's advocate" thing here because it's what I seem to do.
Something that I think is important to keep in mind with stuff like this: Some things, for some of us, simply cannot be changed no matter how much time and effort you put into it. Some things simply go against the way we think... as if it's foreign to our minds and cannot be quite understood.
In my case, being neat and orderly is that thing. I'm 37 (I live with my father & stepmother though) and my room always looks like a mess. Doesnt take long to get it into that state... heck, if I'm in like a hotel room by myself for a trip, it'll look like a tornado went through after about 2 days.
The idea of organizing literally never occurs to me. Hell, the very idea is foreign almost. I look around and think... "but I dont CARE if that object is over there VS over here. It still functions the same, so why waste the time?" That sort of thinking. Now, I *am* a stickler for being sanitized... like handwashing and stuff, and if I were to have a spill on my desk here or something, I'll clean that up. But objects simply being in odd places, or even in a big heap? I'll never deal with that on my own. It never comes to mind. Even after many, many years of parents trying to teach me otherwise.
But here's the really odd thing: I actually tend to feel MORE disorganized when someone comes in and tries to "fix" the mess. Like, my father will come in here and reorganize the hell out of everything every couple of days or so (despite me repeatedly telling him not to). When he does this, suddenly, I wont be able to find things. What looks like a mess to him makes sense to me. So when he cleans it up, I lose track of certain things and get frustrated. Which is another thing I think alot of people dont really grasp. When someone approaches certain things with a very different way of thinking (as many of us here do), the end results can look very strange to others... but that doesnt mean it doesnt serve a function (even if that function is a little screwy).
Even right now, I look behind me, and there's this big pile of seemingly random junk on my bed. All sorts of things in it... some books, a few puzzles, a box of pencils, nail clippers, an entire keyboard.... lots of stuff. The pile gets transferred from the bed to this chair when it's time to sleep, and then back to the bed after I get up. Sounds ridiculous, yeah? But it makes sense to me (though it'd be nigh-impossible to actually EXPLAIN it to anyone). Anything placed in that heap of gizmos is in there for a reason, even if the reason only makes sense to me. The moment someone tries to "organize" it is the moment when things go wrong. I will always end up just rebuilding the pile later.
Overall, what I'm saying is, some things really just cant be changed in our minds. But also, it's important to make sure that you're not trying to put someone into a box they simply dont fit in... it causes nothing but frustration (and possibly meltdowns). Lots of anger and fighting can result from that (been there, done that). Not that this is necessarily what you're doing, I'm just saying it's worth keeping in mind if things just dont seem to be working. Good luck in whatever you decide to do with the situation though.
Oh, welcome to the forums, by the way.