There is this tendency to see younger generations as ideal candidates, however this may be the flaw in thinking. Those who have lived a full life, who know themselves quite well, and have an idea how they may maintain their interests and purpose in an extreme circumstance that has no definite end would likely be more suited for these types of objectives.

Does anyone remember in the old days, when the crews of starships in our science fiction where all in their grey years? When did we swap out mature well developed contenders for such youthful (and less self aware) prospects?

I am not able to endure the psychological torment of Earth...