This is the problem. In the absence of proper diagnostics, people look at popularly touted risk factors like age, alcohol/smoking/drugs, exercise, diet, etc. But these are highly generalised factors that don't take into account: genetic/congenital/epigenetic conditions, stress/emotional issues, environmental factors, and other factors that are difficult to understand by themselves, because the human body is so complex.
The only way to truly determine the extent to which someone's health really is perfect is with detailed individual diagnostics.
As I said in the initial comment, we're only just getting started in developing adequate approaches to diagnosis that may become widely accessible, but I think it's the key to preventing unexpected attacks in your friend and Dustin's friend.