I am 80, and both my parents died of other causes before either developed dementia. Also I am not aware of it in my grandparents who lived to 79, 83, and 86. I did have a great-grandmother who had dementia in her mid-80s but I don't know when it started. I do forget where I put things and appointments if I don't leave reminders everywhere. But what happened that made you realize what it was?