When should I talk to my grandparents about end of life decisions?

65 year old plus. In clinical practice all patients 65 years old and above must have "advance directives" clarified before they present with a serious medical emergency. Pcp's offered on the first appointment or during complete physical exams.
End of life. As painful or difficult it is, the discussions should start as soon as you can. Sometimes adding a neutral party (however you want to define that) is important and can ease things. Even working with a trained attorney that is familiar in these issues is most helpful. Better sooner, rather than later when cognition is affected.