Now now - my 10yo has ADHD, and he doesn't sleep well. Doesn't affect him in the slightest. He is wide eyed and perky all bloody day. I am the one that is wiped out. 
My understanding is that some people need less sleep as they get older. Sleep issues are also a symptom of Alzheimers and/or dementia as is sundowning. I would say it's more likely to be related to that (in my uninformed opinion) 