<a href="https:&#x2F;&#x2F;xkcd.com&#x2F;893&#x2F;" rel="nofollow">https:&#x2F;&#x2F;xkcd.com&#x2F;893&#x2F;</a><p>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.<p>PS: As to reaching age X, <a href="http:&#x2F;&#x2F;www.businessinsider.com&#x2F;social-security-life-table-charts-2014-3" rel="nofollow">http:&#x2F;&#x2F;www.businessinsider.com&#x2F;social-security-life-table-ch...</a>  A 30 year old male has a ~25% chance of reaching 90.  But, these sample sizes are tiny so that does not mean much.