Two Supreme Court Justices who stayed in office until 90 were Oliver Wendell Holmes and John Paul Stevens.
But Senators? It appears to me that only Carl Hayden and Robert Byrd have the distinction of being Senators past their 90th birthday.
This is demonstrably false. Theodore Green of Rhode Island was 93 when he left office in 1961, and of course, Strom Thurmond served until age 100, dying just four months after he left office in June 2003.
A nicer way to term this would've been "Also, Theodore Green of Rhode Island was 93 when he left office in 1961, and as the OP mentioned, Strom Thurmond served until age 100, dying just four months after he left office in June 2003."
But what can I expect, this is Atlas