How long can an elderly person with an untreated case of a staph infection live?

Depends. Depends on what kind of staph, where the site of infection is, whether bacteria is present in blood, where the bacteria was acquired, and the patients comirbid conditions.

Related Questions

What do you treat staph infection with in elderly patients?

Depends. It depends on what staph infection the patient is having. There is so called mrsa, more resistant infection, mssa, less resistant, there are staph infections that are caused by different strains sensitive to different antibiotics. Culture and sensitivity is sometimes done to decide on the choice of antibiotic.
See below. Depends on the symptoms, the location of infection and the sensitivity of the culture to ensure the right antibiotics to treat this condition. It could be oral or IV form.