[Blarg]

It's my guess that a life expectancy of 90 isn't the norm for people who are 50, so if we can't pick people out for longevity by looking at the longevity of their parents and/or family, we'd have to try to find something else concrete to work with. Offhand, I'd guess diet, level of substance use and abuse, exercise, where one lives, stress levels, and wealth would all be very important components in longevity.

In the US, they supposedly live longest in Hawaii. It may not be mathematically sensible to give any 50 year old a 50% chance to hit 90, but I guess if I were to put money on anyone to do it, it would be: A non-smoker who is at most a light drinker and does no other drugs, lives in Hawaii, is retired and has nothing particularly stressful in their life to worry about, has plenty of money to meet any health needs and buy the best healthy food, actually does eat healthy and moderately, and gets plenty of exercise.

Hawaii has a pretty fair number of people who live quite a bit like that.