Final answer:
The client may have posttraumatic stress disorder (PTSD), delayed onset.
Step-by-step explanation:
The client in question is showing symptoms that suggest she may have posttraumatic stress disorder (PTSD), delayed onset. PTSD is an anxiety disorder that can develop after experiencing a traumatic event. In this case, the client's disclosure of childhood sexual abuse and the subsequent nightmares and fear of older men are consistent with symptoms of PTSD.