What needs to be considered is that it's likely that at least two appointments will come open, possibly three over the next two years. One will almost certainly be Chief Justice Rehnquist's seat.
Well, Stevens was born in 1920 so he is 85 years old. Ruth Bader Ginsberg was born in 1933. Bryer was '38, Souter '39. Thomas is the only post WWII person there.