According to my research on studies conducted by medical professionals, I can say that based on the information provided within the question this is all normal. Since Keith is fifty years old, the information provided from the doctor is all normal. If Keith had many neurofibrillary tangles then he would most likely be diagnosed with Alzheimer, but this does not seem to be the case.
I hope this answered your question. If you have any more questions feel free to ask away at Brainly.
