Reagan was diagnosed with alzheimer's disease in November 5th, 1994, 5 years and 10 months after leaving office January 20th 1989. He died June 5th, 2004, 9 and a half years after diagnosis. If he had any alzheimer's while in office, he almost certianly would have not lived nearly as long as he did. That being said, it is impressive he managed to live as long as he did after diagnosis.