I used to be the same way at the same age. I got a ticket for 43 over and I didn't care. I kept driving like an idiot until one time my brakes faded while going downhill and I almost t-boned another vehicle, we would have both been dead for sure as it was over 100mph. There were other close calls before that, but that one did it for me.

I drove like that because I didn't understand the consequences and I had the mind set of "it'll never happen to me" but that changed quickly when I realized I almost could have killed someone else and myself. It took way too long for me to understand that what I was doing was completely fucking stupid.

I took up road cycling recently and that's now my fun activity. It's a whole lot safer, even more thrilling and good for health. So I would recommend maybe promoting a safer activity that would provide him the adrenaline he wants. I don't really have more advice though because I know how it feels to be in that type of mindset and it's honestly terrifying to look back at how I used to have zero value for my own life, and I didn't even realize it at the time. He has someone who cares about him though which is a great start.