While noble to give to the more acutely affected people first, I think distribution at random makes more sense since that decreases the ability of the virus to grow. I'll let the epidemiologists be my guide however.
I believe the theory is, if the virus kills 85-year-old care home residents at 300x the rate it kills healthy under-30s, one dose given to the former is worth 300 doses given to the latter.
Depends on your goal. It the goal is to prevent deaths and reduce hospital occupancy then it make sense to give it to those most likely to die or to be hospitalized. If it spreads asymptomaticly that's not a big deal.
That only makes sense if you don't know anything about who is most at risk.