No, I meant that the young people donate for the old, and that once they turn old there will (hopefully) be more young people to donate blood, again to receive

No, I meant that the young people donate for the old, and that once they turn old there will (hopefully) be more young people to donate blood, again to receive blood from other young people when they turn old. Kind of like a pension scheme (at least the one we have in Germany works that way).