My great-grandmother had a stroke in her 70s, but was pretty functional until she died at 92. My grandmother (same side of the family) is 95, but has dementia. On my dad's side, my grandfather died relatively young (heart issues--he had his first heart attack at the age of 40). My dad's mom, however, is still sharp and upbeat, and lives by herself, despite having had both knees and both hips replaced due to severe OA. She is the "last man standing" out of her siblings, and she's watching her sister-in-law slide into dementia. I don't know how she does it.