I wonder about these longevity clusters and whether they aren't just random. If you've read The Drunkard's Walk, (which I highly recommend by the way) there's a similar phenomenon with cancer clusters and the distribution of shells when the Germans were bombing London.

In both cases people rushed to find some explanation for why the events happened in clusters like they did. What were the Germans trying to target? What's in the water/air that's causing cancer? But if you distribute things completely at random, you end up with the same sort of clusters purely by chance.

So if everyone has a given percent chance of living to a certain age, and it's randomly distributed throughout the world, you'd expect that there would be some clusters where groups of people living a long time show up by chance. It's not quite that simple of course, because longevity isn't independent from one person to the next. e.g. if everyone in your family lives a really long time, there's a good chance you'll live a really long time too. But I'd be curious to see if these clusters happen at a greater incidence than one would expect them to randomly occur or if there's even some way to measure that.