As I point out in my review of James Rosen’s new second volume of his biography of Antonin Scalia, the Court that Chief Justice Warren Burger retired from had its oldest set of five justices ever: all in the range of 77 to 80. That Court, however, fell one gray whisker short of having the oldest overall composition in American history. That dubious distinction (according to my excellent research assistant) belongs to the Court from which Justice Willis Van Devanter retired in 1937. The justices on that Court, right before Van Devanter’s retirement, had an average age of 72.14 years. The Court, right before Burger’s retirement, had an average age of 72.09 years. (The aggregate difference is 181 days, or around 20 days per justice.)
As I also note in my review, the seats of the six oldest justices in 1986 had all been filled by much younger justices by 1994. The Court’s composition, once Stephen Breyer joined it in 1994, would remain unchanged for the next 11 years, the longest stretch in its near two centuries as a nine-member body. (It had a slightly longer stretch from 1811 to 1823, when it was a seven-member body.) You therefore might wonder, as I did, how old that Court was in 2005, just before Chief Justice William Rehnquist died. The average age of the justices then was 71.4 years.
Today’s Court (if my quick estimate is correct) has an average age of 65-1/2 or so. There is a striking symmetry to the ages of the justices. Justice Kagan is the median justice. There is an older cohort of four justices who have birth years twelve (Thomas), ten (Alito), six (Sotomayor), and five (Roberts) years earlier than Kagan’s birth year of 1960, and there is a younger cohort of four justices who have birth years twelve (Barrett), ten (Jackson), seven (Gorsuch), and five (Kavanaugh) years later than Kagan’s birth year. So until the Court’s composition changes, Kagan’s age will be a good proxy for the average age of the justices.