People who are healthiest in their mid to late 30s being more likely to live into old age than those who are not is a plausible explanation for what I have observed.
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.
This suggests a life expectancy of ~78 years old for someone 30 years old today. Of course, as you stated, we'd really need statistics for someone who was 30 years old in the 60s.
John Glenn, Neil Armstrong, Buzz Aldrin, Michael Collins and Edgar Mitchell are all at least several years beyond 78, with Glenn at an impressive 94.
By the way, the life expectancy at birth in that table is 76, so evidently reaching age 30 doesn't actually count for as much as I thought it would.
4 of the 12 people that walked on the moon have already died. If you look at the people who have not died by age X, there life expectancy is going to be based on that age.
People who are healthiest in their mid to late 30s being more likely to live into old age than those who are not is a plausible explanation for what I have observed.