That sounds absolutely terrible. If a villager that old doesn't want to learn just let them do as they please.
How horrible is that to delibrately kill off the elderly.
They are suppose to be your little Islanders who you teach the basics in life so that they can sustain themselves. To see how responsible you are to see just how far you can get in the game.They have made it that long and then to be poisoned just sounds awful.
Most people on this forum love thier little people. They do thier best to keep them alive not kill them off.