What is the average life span after diagnosis of metastatic ovarian cancer that is poorly differentiated?

Varies. Nobody can really give you a specific time period. We usually look at 5 year survival rates. If you know the stage of cancer, you can easily find the corresponding 5 year survival rate on the internet. This tells you what percentage of patients with that stage of cancer will live beyond 5 years. Hope this helps.
Varies. This is difficult to predict in any individual, but the average is probably in the range of 18-24 months.
No answer. It is usually not possible to predict the survival time in a given patient. Generally survival time for a metastatic ovarian cancer is in months, but there are enough exception to make rendering an opinion of exact time a hazardous undertaking.