What stage of Alzheimer's and dementia is my friend at?

We are all learning about Alzheimer's and Dementia because it has touched our lives very deeply. Question is. My former Teacher Jack Who was excellent at His Job, and has been a Life long Friend and Neighbor. Jack is 83 years and was recently diagnosed with Dementia. I had noticed His memory slipping in these last few years hence I knew that it was either Alzheimer's or Dementia since My Mom died from Alzheimer's related illnesses. Recently of late I have noticed anger as Jack is using swear words in sentences which were alien to His vocabulary. In Your opinion WHAT STAGE IS JACK AT? and what is His Life expectancy?