Nevertheless, welfare for olds is in no way an investment when those same individuals have reached the end of their productive years and have a decade or two to live. The point was that calling taxes "an investment" is largely untrue when most tax dollars don't go to anything of the sort.
Social security and medicare are not means-tested in any way whatsoever. In fact, they are massive welfare programs that make our budget structurally unsustainable to give money to the demographic that has had the most time to build up wealth and assets. Around one-third of all US wealth is held by Americans over seventy years old. Perhaps instead of an estate tax, we should explore having those well-off seniors use their savings and home equity instead of demanding government funds. Not to mention decades of subsidizing housing demand has drastically inflated housing prices, and younger Americans are now paying many of these retirees several times what those properties went for decades ago, an increase well in excess of inflation. In other words, through multiple channels, the young are being sucked dry by the old, despite the fact that the old hold a huge chunk of wealth.
I'd also point out old people are a terrible way to feed money back into the economy. They are generally the last people to adopt any innovation outside medicine, so increasing their share of spending draws dollars away from new innovation and towards constructing bingo halls. That has a caustic effect on our long-term economic outlook.
There will of course be the poor grandmother whom we don't want eating dog food. I doubt anyone disagrees with you on that. Let's just not pretend all of them need the checks they presently receive.