@WorriedGrandma Thanks so much for taking the time to provide this update. It does sound like things are trending in the right direction. It is very good to hear he is being properly treated and taking medications to manage the outbursts - this is very important. His parents do sound like they are doing everything they can, which will help over the long term.
Regarding the longer term and growing out of his issues, only time will tell. It does happen although I don't think leaving problems behind entirely is particularly common. I can only speak from personal experience, but I started medications for emotional and outburst control around 5 years old and still very much require them today. Obviously what we describe as an "outburst" manifests quite differently in adulthood, but ongoing treatment is required. Nevertheless, I think depending on the nature of the issue, with appropriate therapy and medications, even if his issues persist, a high quality of life is very possible!