Yeah he has saddle feathers and rust spots on the wings which were pretty good indicators for my boys. Not to mention, he already has a classic rooster tail, curled over with shiny green feathers. most of my cockerels developed those curled green tail feathers, no matter what the breed. Not to mention his beautiful rooster stance!
Also, some cockerels are slow to mature sexually. I have one cockerel that was an absolute angel and basically acted like a pullet until he hit 16 weeks. Like flipping a switch he began harassing and neck grabbing the pullets. So give him time haha