Will anorexia/eating disorders symptoms to loss, trauma happen in the first few months or wouldhappen 12 - 18 months later. if trying to find onset?

Anorexia : Eating disorders, like anorexia and bulimia, can precede the onset of depression, or accompany the disorder. Major Depression may cause lack of appetite or overeating, depending on the case. Usually eating disorders involve a psychological response to your self-image, and cause the behavior of binging, purging or restricting your food intake. Consult with a doctor and a therapist. Both will help.

Symptom latency: Reactive symptoms can have long, medium, short or absent latency periods. Remember, it's not the traumatic event itself but your processing of it that results in the symptom. You might feel a need for an exact onset for paperwork, but what you really need is an off-set date. Try therapy w/ an Eating Disorder expert if possible. It's not easy, but possible and worth it. Best!