My father some days asks me the same question over and over. Is this because he is 87?

Not really only an age thing.. but increased age probably a factor.

Hearing? Didn't hear answer.
Memory? Short term problem.
Anxious? Worry over answer.
Cognition? Didn't understand answer.

That's how my mother's dementia first manifested itself -- the same question over and over.

My Mom has moderate dementia.

She asks the same questions every 5 minutes. Sometimes, recently, it’s every minute. I am not exaggerating.

You may want to out things like UTI, or side effects from meds. Once those things are ruled out, you can figure out what kinds of next steps to take.

Best wishes.

Asking the same question repeatedly may be an early sign of dementia. But dementia can manifest itself in many ways. At his next doctor appt., have your dad screened for dementia. His primary care dr. can do that, and if he suspects your dad shows signs of dementia, he'll be referred to a specialist, likely a neurologist, for further testing.