To whom it may concern:
This thread is for the discussion of Less Wrong topics that have not appeared in recent posts. If a discussion gets unwieldy, celebrate by turning it into a top-level post.
(After the critical success of part II, and the strong box office sales of part III in spite of mixed reviews, will part IV finally see the June Open Thread jump the shark?)
%Centenarians might not be a good metric given that one will get an increasing fraction of those as birth rates decline. For the US, going by the data here and here, I get a total of 1.4 10^-4 for the fraction of the US pop that is over 100 in 1990, and a result of 1.7 10^-4 in 2000. But I'm not sure how accurate this data is. For example, in the first of the two links they throw out the 1970 census data as given a clearly too high number. One needs a lot more data points to see if this curve looks exponential (obviously two isn't enough), but the linked paper claims that for the foreseeable future the fraction of the pop that will be over 100 will increase by 2/3rds each decade. If that is accurate, then that means we are seeing an exponential increase.
Another metric to use might be the age of the oldest person by year of birth worldwide. That data shows a clear increasing trend, but the trend is very weak. Also, one would expect such an increase simply by increasing the general population (Edit: and better record keeping since the list includes only those with good verification), so without a fair bit of statistical crunching, it isn't clear that this data shows anything.