I think we are talking past each other. People who are alive at 30 can't die at 5, but people at birth could die at 5. So, just by being 30+ or 60+ a populations life expectancy increases. Which is why actuarial tables include ages.
So, to see if Astronauts are living unusually longer than other people you need to look at life expectancy's of people who where 30 around 1960's.
Now, they might sill be living longer than that group. But, it does not seem like that's the comparison your making.