Cat peeing outside box

I have a 14 year old male cat that pees outside the litter box every few days. I have three boxes and I keep them cleaned often. I think he's having neurological issues, but perhaps it's something else.
I plan on taking him to the Vet in a few days.
I thought I'd get some feedback from others here first before the visit. This way I can enter the Vet office armed with proper questions.

What have others experienced in this situation?