It's a statistical association, not a rule. I can't say specifically why those two countries have had the results that they have, but the age dependence holds

It's a statistical association, not a rule. I can't say specifically why those two countries have had the results that they have, but the age dependence holds both at the individual and country levels overall. That also doesn't mean that you can't find a 100 year old survivor and a 20 year old that dies from it.