“Alzheimer’s disease” is the term used to explain a dementing problem noticeable by certain changes in brain, regardless of the age.

2. Alzheimer’s disease is a debilitating and progressive brain
disease that causes changes in thinking, reasoning and
behavior. An estimated 5.4 million people in the United
States have the disease and, although it is more common in
people age 65 and older, younger people in their 30s, 40s and
50s can develop it, too.

6. The Alzheimer's Association has an updated list of 10
warning signs of Alzheimer's that I find helpful.