The "senior zone" is immaterial here. The only thing that matters is the sign is properly posted. You're pretty much going to have to assume it is. The only thing that remains to be determined is whether this is a "local road."
If that is the case, you can't avail yourself of the speed trap defense. If it is not a local road (and not in a school zone), then they would need a engineering survey to support the posted speeds.

