My dad has turned 64 and i noticed that he
Dementia is a broad condition and it refers to memory loss. Besides alzheimer's other condition including aging, nutritional deficiency, hormones and so on are causes of dementia.
I understand you are concerned about alzheimer's. We will be able to confirm / rule out alzheimer's after thorough evaluation. Neurologist will evaluate his neurological functions, cognitive functions, mental state followed by battery of blood tests and brain scans. A diagnosis will be formulated based on results of all these evaluation. I will strongly recommend visiting a neurologist as and when possible.
In the meanwhile, it is important that he stays positive. Family and friends support will be crucial to your father's recovery. Fruits, vegetables and vitamin supplements will benefit him.
Hope this helps. Let me know if you need clarifications.