Mental illness or old age??

So most of you know the situation with my grandmother (she has severe myositis and is confined to a wheelchair). Now, I’m getting concerned about my grandfather (who is 81 years old and has been dealing with his wife and her condition for over 7 years). Like I have mentioned in my previous posts, he can get easily agitated and I don’t know if it’s the onset of a mental condition or just old age. Almost every evening, I try to call and talk to him but my grandmother answers and says “he’s outside right now he’ll have to call you later” or something like that. It’s almost like he has adult ADHD (which does run in our family) or something.