Thank you for the query
Dealing and caring an older member in the family can be stressful and difficult.
It is pretty normal to be forgetful at this age.As people get older, changes occur in all parts of the body, including the brain. As a result, some aged people don't remember information as well as what they did. They lose things and forget the usual norms . These are signs of mild forgetfulness, not serious memory problems.
Serious memory problems which affect a persons personality and behavior like Dementia
is when one cannot carry out his everyday activities.From your query I understand that he is able to do his daily activities.This is called Mild Cognitive Impairment
Trying to talk to your grandfather about his misbehavior could help him in understanding the trouble.A care taker's assistance for him can make things simpler and easier especially for his forgetfulness.
If it gets worsened, it is advised to take him to a neuro psychologist
. A neuro psychologist is a licensed psychologist with specialized training in assessment and treatment of cognitive problems associated with dementia or other neurological conditions.
Patience and sense of care is from the other family members , considering his old age will help him a lot.