The “X” were placeholders, like you might see if someone references “Microsoft Windows Version 9.x.x” or what have you. I used them because off hand I didn’t know what version those diagnostic guides were at, when I was in that field it was the ICD-9 and the DSM-IV, I was aware subsequent versions had come out but not which number they were up to is all, hence using the placeholder Xs 
Unfortunately, “issues with the brain” often cause someone to be impossible to live with. They might not respond to reason or logic the way a normal person might. They might have uncontrolled outbursts or fits of rage. They might even be a danger to themselves or others. Just because it’s not a “choice” doesn’t make them easier to get along with.
@MandaJo , I feel like whenever I see your posts they are so thoughtful and compassionate and useful, and this one is no exception <3
Yeah, I agree with this. I also think it’s key for your son to himself acknowledge that this is a problem and that he needs help for it (I can’t tell from your posts whether he actually does think it is a problem). Then maybe you guys can together think of some potential solutions, hopefully involving therapy but even if he refuses that (is there a specific reason why he refuses therapy? Did he have bad experiences with his previous therapists?) working as a team on it. Punching in the face or destroying property is definitely not okay! (Though it sounds like the destroying property thing hasn’t happened since middle school?)
Here’s something my daughter does, that I’ll offer up in case it might be helpful for you: it’s often predictable (if I’m paying close attention) when a meltdown is going to occur with her. The first time something goes wrong (let’s say a computer problem) she’s usually mostly okay with it, maybe a little frustrated (unless she’s already been having a terrible day for some reason – which does happen). If she tries to make it work again, maybe even a third time, and it doesn’t work, or something else goes wrong in close temporal proximity, that’s when she goes full-on meltdown. If I’m paying attention (which is hard, I am often not), I do have a little time in there to help her remember techniques like “okay, when you feel like this, you need to take a break.” (This is complicated by her NEVER wanting to take a break, because something in her brain is like “must do the thing NOW” – but in principle she knows that’s what she’s supposed to do.)
We’ve also been talking a lot lately about how something in my voice, or maybe just that I’m her mom, makes her automatically assume I’m criticizing her, although I’m often not, and that will trigger angry responses (though usually not a full meltdown), and together we’re trying to brainstorm ways around it. The latest brainstorm we came up with (each brainstorm usually only works for a couple of weeks, alas) is for me to pretend to talk like her dad, whose speaking voice is much calmer, which often makes her laugh because I actually am really bad at sounding like him – but really, anything that can make her laugh can often disrupt the kneejerk response.
Also, between my last post and this one, I learned that the daughter of a friend (the daughter is around 20, is still living at home) has just been diagnosed with ASD (which… honestly explains a lot, although she presents very differently from my daughter) and my friend’s daughter is just sooooo happy about it, because it gives her resources and tools. I’m not saying that your son definitively is or isn’t ASD (or, for that matter, ADHD – the child I know who had the most destructive meltdowns, culminating in being kicked out of school for trying to throw a table on another child, turned out to be diagnosed with ADHD and now that he has the right medication is a delightful child), but it’s probably worth looking into diagnosis for all the reasons people have said upthread.
I’m not a parent, and have little I can give you as far as advice, but I’ll say that having him live on his own in a shack in the country, with his right-wing paranoia, sounds like you’re setting him up to be the next Unabomber. It’s too easy for ideations (right-wing, fundamentalist religions, Islamic jihadists, etc) to be cultivated when all you have is an already mentally ill young man and a computer.
Perhaps you could make him more responsive to psychiatric testing by explaining to him that a diagnosis might help him get disability money. Also, all of this isn’t fair to your younger son. I know, having a disabled family member always puts stress on those in the family that aren’t disabled, but do think of him when you’re considering counseling and therapy. He may need someone to talk to, too.
Also, I have a friend who has a son on the autism spectrum, and although of above-average intelligence is developmentally delayed. She told him delayed may mean things happen slower, but they will happen. For example, once he was an adult, she told him it was his responsibility to provide dinner for the family one night a week. She didn’t care whether he cooked, or picked up take-out, he needed to provide dinner on Wednesdays. He had a great deal of trouble holding down a job, because he always knew better than his supervisors how whatever job should be done. He finally found a job he could do, a night job at home on his computer. Eventually he moved to his own condo. His parents helped him out, but he’s holding his own. Basically, it was baby steps moving him in the right direction and not letting him fall back on his diagnoses. He was almost 30 before he moved out, but he did become a decent adult.
StG
This, so much this.
I’m really curious about the long stretches of no meltdowns – is this common for children with these sorts of issues? I would expect mental health problems to be consistent so I’m wondering why long stretches of managing with bursts of meltdowns. I know we all do this to some extent, being more upset one day by something we normally take in stride, but for most of us it’s a fairly narrow range, we either trigger easily all the time, or rarely, and it’s fairly easy to pinpoint the causes for the rare events. So why is it so different for these kids? Hormonal? Environmental? Amount of sensory input? Another commenter mentioned there are signs preceding their child’s meltdowns so also wondering if this is standard (sure would be helpful). I don’t have any theories, just struck me as odd so I’m wondering. I did a light search for information and found little – but did find lots of advice for handling autism meltdowns in adults which might be useful.
I think it is pretty common. I know my kid is like that. Too tired, too hungry, too stressed from other things, and a minor setback can cause a meltdown. We can go days without a meltdown, and then something seemingly trivial can cause a huge blow up.
Today for example, Minecraft was crashing. She came and nicely asked me to help her get it going. Frequently when that happens there is screaming, banging, and declarations of never playing Minecraft again. What was different?
Thanks… everything I find on this addresses autism related meltdowns and all suggest the cause is sensory overload, either too much at once, or cumulative. The unpredictability alone must add a level of stress for parents.
He’s usually ok as long as his routine is not broken. But any problem that for most people would be a minor annoyance sends him into meltdown mode- the internet going down, the power going out, problems with his computer, etc. Even when the A/C went out during a hot stretch this summer- he acted like he was dying of heatstroke. The house naturally stays cool and the temp never went over 81 inside even when in the 90s outside.
Does your son have any history of head injuries or TBI? Has that been ruled out as a potential cause.
So he’s a bit of a drama queen 
Those who have meltdowns point out that the event is much worse for the person having it than those watching – the loss of control is frustrating, horrifying and embarrassing. That makes sense and I’m sorry your son has to go through this. Our society really has little to offer, what programs exist are overwhelmed, you and your wife are truly wonderful for trying your best to help your son and I hope you can find the help your family needs.