What is the life expectancy for someone with stage 4 kidney disease?

Ask your oncologist: This is a complicated question that no doctor can answer with the facts of your case. It depends on your response to your medical treatments.

Possibly many years: Life expectancy depends on the rate of progression (many factors including medical and lifestyle interventions that might slow down the progression) and decisions on whether to pursue renal replacement therapy once reaches end-stage (that decision may depend on overall health, functional status, ability to tolerate various interventions, etc). Overall shorter than the average public lifespans.