The onset of an anxiety disorder or a panic disorder with or without Agoraphobia could be at any age. Statistically the onset for panic attacks is most common between the ages of 25 and 30 years and Agoraphobia somewhat later (approx. 6 months).
Unfortunately, despite of all information, it usually takes a very long time until a qualified diagnostic and treatment begin: Most patients wait until the age of about 36 before they get help. During the intervening years, the patients try to cope with the panic disorder by developing more or less suitable avoidance strategies.
Characteristic for the panic disorder is the panic attacks and that they can occur in random phases. Patients report on longer existing phases in which no, or very few, panic symptoms were present. New or difficult situations could be triggers for a new panic attack after a long symptom-free period.
It is quite typical that the first occurrence of panic symptoms is believed to be a physical illness or pure exhaustion. After maybe several weeks or months, if panic symptoms occur again, the victims are not sure that the new attack is connected to the earlier symptoms. It could be important though, for the psychotherapeutic treatment of the panic attacks to remember when and how the first panic attack occurred. Hopefully this can give some advice about causes and problems to investigate further on in the therapy process.