Welcome John, thank you for caring, so many parents make zero effort to understand their autistic children but you're a good father. It's fine to ask for help here, nobody's going to bite your head off like they will pretty much everywhere else on the internet, but future inquiries you might want to post in "General Autism Discussion"; you'll get increased exposure, more than you'll get in the Intro section.
I have no way of knowing how much you already know, so if you'll forgive me I'm just going to spill everything I have to say on the subject:
In terms of Andre's recent aggression, from what you describe my theory is that it's a convergence of three factors.
1) The Hormonal Aspect: Males reaching sexual maturity get huge boosts of testosterone, which we all know heightens aggressive behavior. Most teens just turn into "little alphas" but I'd wager that, combined with the other two aspects, increased hormone levels are the fuel behind the aggression while #2 and #3 provide reasons why. Side note: does he have acne on his chest? That's probably the best way to tell yay or nay on high testosterone without a laboratory test, which you may also consider. Also worth noting is that the hormonal aspect of puberty tends to hit like a ton of bricks rather than gradually - some sooner, some later. That's the best explanation I can think for the rapid change in behavior between 15 and 16, a short time indeed.
2) The Genetic Aspect: Many people with autism have low levels of activity in the MAO-A enzyme, aka The Warrior Gene. This can result in unexplained aggressive behavior or violence disproportionate to the situation. This article, "
About The Warrior Gene (MAOA) And What To Do If You Have It - Selfhacked" explains the links between weak MAO-A activity and aggressive behavior, the most interesting of which is: "the perfect violence soup is low MAO-A, social isolation, high testosterone"; incidentally all three convergent factors I'm mentioning. Also, if he has at least a moderate tremor, that can indicate high serotonin levels which can be a telltale for low MAO-A activity.
3) The Social Frustration Aspect: I can almost guarantee that Andre wants to talk to other people, but one thing or another is preventing him from being able, which I can say is very frustrating; I was selectively mute from ages 12-19. I vividly remember people speaking to me, and I wanted so incredibly bad to say something, but I just couldn't make the words come out of my mouth. Usually I'd panic and bolt, but if I felt that wasn't an option I would get really frustrated and sometimes have a meltdown.
As for the self-injurious behavior, I may speak from experience that biting is a much more effective way to release the overwhelming tension than any other form of self-mutilation. That's probably why he's doing it. Ditto with the head banging; I'm willing to bet he's probably rocking back and forth many of the times when he head bangs?
Something that's very telling to me is that you don't say he's violent towards others, just angry with frustrations and outbursts. This tells me he may be having the teen version of a meltdown like you say, which looks different than it does in children; usually by that point people with autism have learned to keep at least some measure of control during a meltdown, but with the agitating factors mentioned above may be more aggressive and focused in nature. Especially the case with the high testosterone, I've abused testosterone before and it just kind of puts you in this red haze of rage at all times.
WELL THEN, that's a whole lot of "what and why", but as GI Joe says, knowing is half the battle - only half the battle. Maybe I can offer some advice on how to help.
1) Hormonal Aspect: usually screwing with testosterone/estrogen is a really bad idea. There are supplements that will lower testosterone, but don't bother; hormone altering drugs are effective in the short term, but the body will upregulate or downregulate natural testosterone production, so after a couple weeks you might as well be swallowing Sweettarts because you'll be right back at square one.
What I would do about this is to talk to his doctor and ask for a test for testosterone levels. Usually a doctor won't disrupt the natural processes of puberty, but it's possible his testosterone levels are problematically high. See if they are and go from there.
2) Genetic Aspect: This is the hard one. From the medicinal standpoint, there are two things that must be done in sequence: First, serotonin levels need to be decreased. Arguably, a gluten-free diet can at least do part of the job. I'm not sure, but an MAOI antidepressant that acts on the MAO-A enzyme would probably be the most effective medication, and the only one I can think of. Unfortunately, most doctors only prescribe MAOIs as a last resort only for severe depression. A tiny percentage of people experience life-threatening side effects with MAOIs, so doctor's don't want to take the risk being held liable for that and only prescribe the 100% safe meds that don't really work.
The reason serotonin levels must be lowered is because serotonin inhibits the development of oxytocin nerves, which are "needed for language development, bonding with others, and social skills, language development". Do what you can to lower serotonin and hopefully more oxytocin nerves will develop. I say hopefully because not much can help increase oxytocin levels; Buspirone (Buspar), an easy-to-obtain anti-anxiety medication might do it. Otherwise, all I can think of is substituted oxytocin, aka opiates, but that's really playing with fire. It may also be worth noting that oxytocin is found in the thyroid, which is underactive in many with ASD. I'm not sure exactly how much, but if Andre is one of us with low thyroid activity treating it may contribute. Testing thyroid levels is a simple blood test, and fixing it is 6 drops of
nascent iodine daily with Selenium for safety.
3) Social Frustration Aspect: There are a few things you could try. For the non-verbal part of it, try this: catch him when he's calm, and just have a one-sided conversation with him. Make sure to be calm and keep undue pressure off him to respond. If you hit a point where it would be natural to pause for a response, count two seconds in your head and then continue. Don't ask too many questions. The point of all this is to give him opportunities to speak, but only if he wants to, without feeling that he has to even though he cannot; the point further being to keep him from getting so frustrated it triggers a meltdown. Don't tell him what you're doing or he might just wait you out. He may not speak much or at all, but the words are in his head; I doubt he just thinks in wordless impulses like an animal. He'll talk eventually.
As for the self-injury, there's no way to get him to stop, unless you take extreme measures, the choice to do so is his (note: disinfect the crap out of the bites if they break the skin, a human bite is one of the most toxic bites in nature). I would bet he only self-harms when he's upset, so the only way is to stop the meltdowns and subsequent self-injury is by addressing the three aspects I outlined.
Finally, I have to address a concern I have. With everything you described, I'd say Andre is at a high risk of being put on antipsychotics. If it hasn't happened already, someone's going to try to talk you into it. 8 years of feverish research and personal experience tells me that this class of drugs is completely useless except as a chemical restraint, and that's all they're used for. Being too sedated to lift your head is not "behavior well-managed with medication".
I just say because I feel passionately against the rampant use of antipsychotics to induce compliance by destroying a person. I used to work with medical records of developmentally disabled children in a large inpatient psych facility. I had to read the whole file for each kid, and I was especially interested in the autistic kids. With them, it was so common to find an incident report describing a meltdown as a "tantrum", where the staff did everything they could to make the situation worse, and as a result recommended an increase to the haloperidol that literally every single kid in that place was on. It broke my heart, seeing the name and face of every kid and knowing they were all kept chemically restrained for the convenience of staff. I'm made to understand that this is the general unwritten policy for most psych hospitals, and that needs to change.
Well, that's what I have. Feel free to contact me if you need anything.