Hello,
the straight answer is that it could be
dementia. Many old people experience difficulties with their every day tasks like remembering a new piece of information (the name of a new neighbor or to buy milk). This is the normal aging process. Dementia is an accelerated form of this decline.
Your father is not that old. Actually he is not old enough to attribute his difficulties to an age-related cognitive decline.
Dementia does not spare the younger individuals though. It usually starts with cognitive decline of some sort, barely apparent at first but progressive during its course.
It could be forgetfullness, which is common but it could also cause difficulty in every day activities even motor ones (not only related to thinking that is).
Your best next step is to visit a
neurologist who will be able to conduct clinical and radiological tests to your father, in order to confirm or rule out the diagnosis.
When assessing a patient for dementia, the doctor should rule out other conditions that may contribute to cognitive decline like tumors, vascular problems, medications etc
I hope I've shed some light on his condition.
If you need further explanation of the subject, please ask and I'll be glad to provide it for you.
Kind Regards!