Gosh, it's hard. I have two sons that are just a year apart in age. When they were little, we did things like "everyone gets a turn to win" or if someone wanted something the other had, they had to make a trade to take it. And that everyone got a chance to choose and we took turns. I'd start maybe doing some of that and reward with praise when he is caught doing anything positive with his sibling! We used beans that we put in a jar too for these things and when he got to 6 beans, he got to have a reward like picking the movie we watched or a cookie or something.
I had a brother who was 41/2 years older than I was, and he was a very frustrated guy who took it out on me. Our play always ended with him basically beating me up. As you can imagine, this didn't lead to a good long-term relationship. My parents never did anything about it, and when my Mom did, it was usually to punish me, for some reason, probably because I would end up crying. Of course I got older and we stopped playing together and that solves the problem, but I would have liked to have had a good relationship with my older brother. But the hard part is, young kids just accept what's going on as normal even if it's not what they like, which is how I responded -- it never stopped me from wanting to play with him, but again, it did lead to problems down the road when we got older. I don't believe the problem was with my brother, it was with my parents for not doing anything about it, so my suggestion would be to try at least to see if you can interrupt this behavior with gentle encouragement. I think my brother could have used some of that so he didn't feel frustrated and didn't feel jealous about a new child coming along.