Originally Posted by Idigmygirls

A shadow is not an actual thing. It is the absence of light. More specifically, it is the area of a surface that is obstructed by an object that exists between it and a light source.

Understanding that, you should be able to see why your premise is incorrect. The light source generates photons that travel at the velocity of light. When a shadow is "cast" it means that some of the photons are blocked, while others are not blocked.

The unblocked photons arrive on the surface at the speed of light. The blocked photons do not arrive. This creates a shadow, which, by definition, is created by the photons that are not blocked. Since those photons travel at the velocity of light, the shadow is created by the absence of photons - at exactly the speed of light.