Mid Cerebellum &cerebral; atrophic

My father is 77 years old with no history of blood sugar and bp. He has always been fit and walks almost 5-10 km daily. For the past two months he has been feeling weak, tired, pain below both the knees and even left shoulder. For the past three days he has been feeling really dizzy and even finding it difficult to walk, specially in the morning. We just got a brain ct scan done and it says - the basal cisterns, fissures and suici are prominent. Ct findings reveal mild cerebellum and cerebral atrophic changes. Advise mri brain and clinical correlation, what does this mean ? I consulted a general physician- after checking him physically he said it's mostly old age and exertion due to doing a lot of physical activity and he should rest - and consult again if needed. What should I do? His blood sugar, kft , crp , cpc, liver tests are normal. He still feels dizzy at times