How long can a elderly and after a stroke stay alive on a peg tube?

Nobody knows exactly: Unfortunately we can't predict death that time and day is so unknown to human at this point even with cancer we can give a majority( stat significant) 5 year survival rate but that is not true for every body but something like stroke which in itself not consuming the body as cancer is is not predictable now with fracture femure and hip they have studied and in couple of years after the fall and.

Can't predict: A peg will provide needed nourishment for as long as he lives. This will be determined by his underlying illnesses and their seriousness. A patient with a mild stroke can be retrained to eat normally. Patients with severe strokes may succumb to other problems, such as pneumonia or even a second stroke.