Who is considered the oldest justice to sit on the US Supreme Court?

Associate Justice Oliver Wendell Holmes Jr. (1841-1935) is considered the oldest person ever to sit on the US Supreme Court. He served from 1902 to 1932, (and as Acting Chief Justice from January–February 1930). Holmes resigned due to ill health in 1932, at age ninety. He died on March 6, 1935, barely two days short of his 94th birthday, and was buried in Arlington National Cemetery. He was the son of Oliver Wendell Holmes, Sr. (1809-1894) who was a physician, a professor of medicine at Harvard, and an author of novels, verses, and humorous essays.

Justice Holmes was appointed by then President Theodore Roosevelt to the bench, where he became known as “the great dissenter”, because he was often at odds with his fellow justices. However, he was praised for being capable of eloquently expressing his dissents. He is one of the most widely cited Supreme Court justices in American history, particularly for his "clear and present danger" opinion, not just because he wrote so well, but also because he wrote so much, and for so long. Any lawyer seeking a quote from Holmes is never left wanting.

Justices appointed to the US Supreme Court have life tenure, which means they serve until they die, unless they resign or retire, or are removed from office by way of impeachment. The longest serving justice was Justice William O. Douglas at 36 years. The youngest associate justice ever appointed was Joseph Story, who was 32 years old when he joined the bench in 1811.