I’m not sure this is actually aggression, at 5 months he could just be playful. Kittens will “play fight”, just like lion or tiger cubs will, to hone their hunting skills. Are the other cats playing back? By playing I mean will they wrestle with him? If they are hissing, or the fur on their back is standing up.. they are not playing. Otherwise, it could all be in good kitty fun. Neutering should calm him down overall.