There is considerable variability in the population and many individuals have much loss of kidney function. But on average a linear decline in the GFR occurs after the age of 40. Other functions like glucose resorption are also decreased in the aged. This decrease in GFR means that, for drugs excreted by the kidney, the doses of drugs need to be adjusted to compensate for the age-related decrease in renal function. The loss of nephrons also results in a decrease in the production of renin and secondarily, aldosterone.
Hyperkalemia is just one of many causes of hypertension in the elderly.
Hypertension and edema are common and, in worse cases, protein and blood can be found in the urine. The treatment is with antibiotics for bacterial infections and steroids to reduce the inflammation. Abdominal aortic aneurysms are often associated with occlusive disease. The most common event in older persons is renal failure secondary to heart failure. The most common therapy for chronic renal failure is hemodialysis.