It is interesting who signs up for Obamacare and who doesn't, but the idea that we need the "young invincibles" to save the program is just flat out wrong as a recent analysis by the Kaiser Family Foundation showed. For this reason it was disappointing to see this piece by Sarah Kliff in Wonkblog this morning.
There is a big issue as to whether enrollment is skewing by health. If sick people disproportionately sign up for the program then it will make its finances untenable. But age really doesn't matter much in this story. A healthy older person will on average pay three times as much to support the program as a healthy young person, with neither getting any significant payback since they are healthy.
That's the arithmetic, it's about as simple as it gets.