Dianne Feinstein (D-CA) is running for re-election in 2018 at the age 85. [View all]

[nkpolitics1212]

Here is a list of US Senators who were over 85 years old when they ran for re-election and won.
Strom Thurmond (R-SC) 87 years old in 1990,93 years old in 1996. served 48 years in the US Senate.
Robert Byrd (D-WV) 89 years old in 2006. Served 51.5 years in the US Senate.
Daniel Inouye (D-HI) 86 years old in 2010 Served 50 years in the US Senate.
Unlike Thurmond,Byrd,and Inouye-Feinstein will not get a chance to be Senate President Pro Tempore.
Feinstein is the 2nd most senior Democratic US Senator after Pat Leahy (D-VT). In order for Feinstein to be US Senate President Pro Tempore, Democrats will have to regain control of the US Senate by 2022 and Leahy will have to retire in 2022.
Pat Leahy (D-VT) could be the longest serving US Senator. He wins re-election to a 9th term in 2022 at the age 82, 10th term in 2028 at the age 88, and 11th term in 2034 at the age 94.