RDU Controller described a MOA restricted airspace separation event when a developmental was late in issuing corrective vectors to the aircraft in question.

Narrative

OJT was being conducted on combined positions NDR/SDR. Aircraft X checked on frequency and requested a deviation to the east to have a look at something Northeast of HRJ airport. The Seymour Johnson ECHO MOA was active. The trainee obtained approval from FAY for turns and approved the pilot's request. I then asked the trainee if there was a potential problem and he told me of the MOA. I let the aircraft get to a point that I wasn't comfortable anymore and told the trainee to turn the airplane. He did and the pilot delayed his turn. I then told the aircraft to start his turn now. I am not sure if we had less than the required 3 miles from the boundary; but it was close. After corrective action was taken; the trainee explained to me he thought he only need 1 1/2 miles from the boundary. There were not aircraft observed near the MOA boundary at the time of the incident. Recommendation; in retrospect; the request should have been denied until such time as coordination was effected with Seymour Johnson or had the aircraft descend to an altitude below the MOA after coordination.