Things that can kill a 70 year old include such threats as falling over, or moderate exercise. At no point in thousands of years of human history have we seriously tried to keep all the 70 year olds who were alive at the start of the year alive at the start oft he next year. It isn't possible.

60s is a different thing, but at 70 there are very real questions about whether a quarantine is even worth it. Do you risk losing half your remaining lifespan in a quarantine, attempting to avoid a 30% chance of death? The calculus is grim, but that doesn't mean it should be ignored.

Would you rather the “over 0s” do that instead?