I'd be surprised if there's a single person alive who would volunteer for a suicide mission to a miserable cold dark planet and could travel there for nine months in a tin can through a harsh radiation/muscle atrophy/psychological environment and arrive in any condition to conduct useful scientific work.

Can we trust them to enough? If they have a medical emergency (which is quite probable, old people are in risk of all kinds of trouble, even before the harsh environment of spaceships), will the whole mission fail?

We generally have selected the most vigorous military personnel to participate in these types of missions, using old volunteers would be quite a change.

I've been excoriated for making that suggestion.