If a cockerel the tail feather will grow up and eventually down. The neck and saddle feathers will be longer and pointed in downward position as grows. The combs, wattles will be bigger and redder. The feet bigger if a male.
The biggest question with Brahmas is age. All three of my brahmas grew weird tail feathers, before they had that first molt, so that's not a good judge. And they won't grow male or female saddle feathers until they're about 13 weeks, since they're slow to mature.