Today, aging and dementia are the flip side of life tenure, with more and more judges staying on the bench into extreme old age. About 12 percent of the nation's 1,200 sitting federal district and circuit judges are 80 years or older, according to a 2010 survey conducted by ProPublica. Eleven federal judges over the age of 90 are hearing cases -- compared with four just 20 years ago. (One judge, a Kansan appointed by President John F. Kennedy, is over 100.) The share of octogenarians and nonagenarians on the federal bench has doubled in the past 20 years. The demographics of the federal bench have no analogue on the state courts, where judges mostly occupy their office for a term of fixed years and generally have mandatory retirement ages, often in their 60s or 70s.