> My theory on the 50+ for mars missions would mainly be due to radiation
> induced cancer risk. If the mars mission causes you to have cancer in 30
> years well from 50 that "aint so bad" as if you send a 20 year old and
they
> get it at 50.

That's NOT the major reasoning - just a bonus.
On a long trip (and the 1st Mars mission would last 2 years + using minimum
energy Hohman transfer paths), the ability to survive as a group is a major
factor. Selected "oldies" are seen as more likely to do so.

Plus all the things that others have suggested.

The things which make oldies unattractive to those seeking intelligent
cattle fodder to help them make their fortunes can be what's required when
the task involves sole charge of a small world where the right decisions
have to be made instantly (such as part way to the Moon, or in a slightly
faulty vertically climbing rocket ship somewhere above the Mojave, or
somewhere slightly west of Olympus Mons).

You still have to select your oldies well of course :-).
Arguably (very) you may get a higher percentage of high class young un's
than oldies, BUT the best oldies are derived from the best young uns with a
few decades of life skills added.


        RM

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