I am tempted to say a cockerel, and I have been in this situation before as well. With the walnut comb, which is most common in silkies, it makes sexing increasingly difficult.
The darkening hackle feathers are an indicator of a roo, but for me, have proven unreliable. I had a hen look exactly the same--somewhat large comb and wattles, with king of golden hackles--she is a white bearded silkie.