Posting here for traffic as every time I've posted a thread somewhere else responses are very limited.
DS (9) is a lovely, loving, cheerful little boy. He's great with smaller children and babies, loves animals, very kind and accepting, he's well-liked and does well at school, quite stoical with any sort of pain or accidents, in many ways just socially/emotionally very well-adjusted. He also loves DD (11) fiercely and sometimes they play really well together. He can set boundaries and is polite, sweet, has a lot of empathy. In general just a really lovely little boy.
However, his sibling rivalry with DD is also pretty fierce (which I know is common) and there are some blazing rows which get out of hand, especially when we play games and his sister wins (but even if anyone else wins it can happen). His voice gets very high and almost panicky, as if his nervous system is completely overloaded. He becomes highly sensitive and completely, almost comically unreasonable (except there is no opportunity to find humour in the situation as it's always very stressful). He starts throwing things and screaming. Whether we tell him gently or forcefully that this behaviour is unacceptable, his behaviour only gets worse and I can see that he becomes incredibly distressed, to the point where even attempting to offer comfort triggers more agitation. We impose consequences like banning the game that caused issues, but it doesn't seem to have made any difference. I keep telling his sister he'll improve but he's been stuck at this level for years now.
The main thing that worries me is that when I try later to quietly talk to him about his behaviour, he deflects and says it's everyone else's fault. He cannot seem to reflect at all, he just flips out and goes straight back into fight or flight mode. He also has a victim mindset of being the one the rest of the family are all against. I worry this will impact on his ability to take accountability and on his sense of belonging to the family.
The nursery he was at thought he was possibly ND but an evaluation revealed it turned out he had a significantly higher than normal IQ. This isn't a brag, just to give context as higher IQ can cause children to have exaggerated responses to stress and social difficulties.
Will he grow out of this? Did anyone experience a similar situation which resolved? What helped? What made it worse? Am I expecting too much of a 9 year old boy? Is this just normal?
Any advice/help would be really appreciated :)