The most important thing you need to understand is
sugar and blood pressure are leading causes of
kidney failure if they are uncontrolled then thier is high probability of getting a kidney disease and after 40 years of age the kidney function keeps falling down one ml every year in case of your father his gfr may be low but he's with in normal limits for his age
Next Steps
low salt diet ,45 mins of exercise every day ,0.5 to 0.6 gm protein would help you prevent disease
Health Tips
avoid painkiller and any other alternative nephrotoxic Medications