Quick history lesson on the senate from Wikipedia~
Qualifications-
Article I, Section 3 of the Constitution sets three qualifications for senators: 1) they must be at least 30 years old, 2) they must have been citizens of the United States for at least the past nine years, and 3) they must be inhabitants of the states they seek to represent at the time of their election. The age and citizenship qualifications for senators are more stringent than those for representatives. In Federalist No. 62, James Madison justified this arrangement by arguing that the "senatorial trust" called for a "greater extent of information and stability of character."
The Senate (not the judiciary) is the sole judge of a senator's qualifications. During its early years, however, the Senate did not closely scrutinize the qualifications of its members. As a result, three senators who failed to meet the age qualification were nevertheless admitted to the Senate: Henry Clay (aged 29 in 1806), Armistead Thomson Mason (aged 28 in 1816), and John Eaton (aged 28 in 1818). Such an occurrence, however, has not been repeated since.[20] In 1934, Rush D. Holt, Sr. was elected to the Senate at the age of 29; he waited until he turned 30 (on the following June 19) to take the oath of office. In 1972, Joe Biden was elected to the Senate shortly before his 30th birthday, but he reached his 30th birthday in time for the swearing-in ceremony for incoming senators in January 1973.
Election-
Originally, senators were selected by the state legislatures, not by popular elections. By the early years of the 20th century, the legislatures of as many as 29 states had provided for popular election of senators by referendums. Popular election to the Senate was standardized nationally in 1913 by the ratification of the 17th Amendment.
Elections to the Senate are held on the first Tuesday after the first Monday in November in even-numbered years, Election Day, and coincide with elections for the House of Representatives. Senators are elected by their state as a whole. In most states (since 1970), a primary election is held first for the Republican and Democratic parties, with the general election following a few months later. Ballot access rules for independent and minor party candidates vary from state to state. The winner is the candidate who receives a plurality of the popular vote. In some states, runoffs are held if no candidate wins a majority.
Oath-
The Constitution requires that senators take an oath or affirmation to support the Constitution. Congress has prescribed the following oath for new senators:
I, ___ ___, do solemnly swear (or affirm) that I will support and defend the Constitution of the United States against all enemies, foreign and domestic; that I will bear true faith and allegiance to the same; that I take this obligation freely, without any mental reservation or purpose of evasion; and that I will well and faithfully discharge the duties of the office on which I am about to enter. So help me God.
Expulsion and Disciplinary Actions-
The Senate may expel a senator by a two-thirds vote. Fifteen senators have been expelled in the history of the Senate: William Blount, for treason, in 1797, and fourteen in 1861 and 1862 for supporting the Confederate secession. Although no senator has been expelled since 1862, many senators have chosen to resign when faced with expulsion proceedings – for example, Bob Packwood in 1995. The Senate has also censured and condemned senators; censure requires only a simple majority and does not remove a senator from office. Some senators have opted to withdraw from their re-election races rather than face certain censure or expulsion, such as Robert Torricelli in 2002.