There may be some long-term bias going on here. It would be interesting to see what correlation there is between current age and preferred age of death. You'll might find that 60 year olds (with death only 20 years away) would answer differently to 18 year olds.
Can you point me to where it says this in the article? Because I don't see it - he mentions talking to people from "all walks of life", but that's different to having no correlation.
>These percentages have held up as I’ve spoken to people from many walks of life in libraries and bookstores; teenagers in high schools; physicians in medical centers; and investors and entrepreneurs at business conferences.
The percentages are the same for groups of teenagers, and for groups of physicians investors and entrepreneurs. There could be a jump at 60+, but based on his data there isn't a difference between teenagers and working adults.