Stop right there.
You probably know what's coming: Kinsley is citing the average net worth rather than the median. But of course, wealth in the United States is fairly concentrated at the top; it's not as top-heavy as Colombia or Mexico, but it's top-heavy nonetheless. The median household age 65-74, also according to the Fed, has a net worth around $209,000. The two figures are right next to each other on table, so Kinsley really has no excuse. To get to a net worth of $650,000 you have to go all the way to the top 25% of U.S. Households, and that's still a figure that most retirees will spend down almost entirely by the time they die. The data suggests that what Kinsley really wanst is either an extremely high threshold for Social Security means testing (basically, if you qualify for whatever reformed AMT we end up with, you don't get your Social Security Check) or the estate tax, not a sudden shift to eliminate Social Security benefits for the middle class.
Hopefully Douthat will have an easier time spotting the next time the economic royalist wing of his party tries to pull the wool over his eyes with crappy data.