November 16, 1818
When the Senate convened on November 16, 1818, it set a record that is never likely to be broken. Members on that occasion, however, probably did not realize they were making history—and violating the Constitution—in administering the oath of office to Tennessee's 28-year-old John Henry Eaton.
The framers of the Constitution set the minimum age for Senate service at 30 years. They arrived at that number by adding five years to the 25-year minimum they had established for House members, reasoning that the deliberative nature of the "senatorial trust" called for a "greater extent of information and stability of character" than would be needed in the House.
Apparently no one asked John Eaton how old he was. In those days of large families and poorly kept birth records, he may not have been able to answer that question. Perhaps it was only later that he determined the birth date which now appears on his tombstone, confirming his less-than-constitutional age. Had someone in 1818 chosen to challenge his seating, Eaton could have pointed to the Senate's 1816 decision to seat Virginia's 28-year-old Armistead Mason, or the 1806 precedent to admit 29-year-old Henry Clay.
Within a few years of Eaton's swearing-in, the Senate began to pay closer attention to such matters. This issue then lay dormant for more than a century until the 1934 election of Rush Holt, a 29-year-old West Virginia Democrat. During his campaign, Holt had pledged to wait six months into the 1935 session until his 30th birthday to be sworn in. While he was waiting, his defeated Republican opponent, former incumbent Senator Henry Hatfield, filed a petition with the Senate charging that Holt's failure to meet the constitutional age requirement invalidated his election. Hatfield therefore asked that he be declared the winner, having received the highest number of votes among other eligible candidates.
The Senate dismissed Hatfield's arguments, observing that the age requirement applies at the time of oath-taking rather than the time of election, or the time the term begins. It also reiterated that the ineligibility of the winning candidate gives no title to the candidate receiving the next highest number of votes. On June 21, 1935, Holt followed in the line of Eaton, Mason, and Clay as the Senate's fourth youngest member, beating by 28 days the fifth youngest member, William Wells of Delaware, who took the oath of office in 1799. In January 1973, the distinction of becoming the sixth youngest—and the youngest since Holt, at the age of 30 years, 1 month, and 14 days—went to Delaware's Joseph Biden.
McKellar, Kenneth. “John H. Eaton.” Included in Tennessee Senators as Seen by One of their Successors. Kingsport, Tenn.: Southern Publishers, Inc., 1942).