By far the most common defense of the Kagan pick in our comments sections has been to cite her age. Indeed, several regulars have made the claim that Diane Wood’s age should obviously have eliminated her from consideration. I think this is utterly silly, and is a case in which conservatives are much more savvy than liberals. If you look at life expectancy charts, Wood can essentially expect to live as long as Sam Alito. Does anybody remember Republicans outraged about the Alito pick, urging Bush to pick somebody who didn’t have impeccable conservative credentials so that they could get someone a couple years younger? Neither do I, and in this case the Republicans are obviously right. Within a plausible range of options, the age of nominees isn’t that big of a factor. The key things limiting its importance are that 1)it’s most important that justices be replaced by someone with similar values and 2)there’s a modern norm that justices resign when they can be reappointed by someone congenial. Given these two things, within reason the age of nominees doesn’t make all that much difference. In the most common case, a judge simply resigns and allows a president to pick someone similar who can serve a lot longer.
And even in cases where judges leave under conditions not of their choosing, sometimes it doesn’t matter. Rehnquist passed away in office, but was replaced by a near-xerox anyway (and may have resigned had Bush not been a favorite to win re-election.) Brennan and Marshall were replaced by Republican appointees (one OK and one a very young reactionary), but this just proves that if you don’t win a lot of presidential elections it’s going to be hard to keep ideologically congenial people on the court; there was only a four-year window between 1973 and 1992 in which they could have resigned and been replaced by a Democratic appointee. Black and Douglas left immediately before passing away, but here again it would have been better if they had been a little older, resigned and were replaced by LBJ (especially Black, who got cranky and more conservative in his last decade.) Harlan left under similar circumstances, but since he was replaced by Rehnquist it’s hard to say that this didn’t work out well for the Republicans.
In addition, relative youth is only a significant advantage if it’s clear that a justice will be a reliable vote. Thomas’s youth worked out well for conservatives — but Souter’s didn’t. Since we have no idea whether Kagan will be a reliable vote or not, her relative youth is much less of an advantage. When you combine this with the fact that being ten years younger will only matter in the long-term under a very unusual set of circumstances, the idea that Kagan is a better pick that Wood because she’s younger becomes untenable. Age might matter all things being equal, but that’s not the case here.