There are now four octogenarians and one nonagenarian in the U.S. Senate, where more than half of the chamber is over 60.

The big picture: Sen. Dianne Feinstein of California died in office at 90 last year, as America's aging leaders have been on display, prompting conversations around fitness for office, term limits and ageism.

• Sen. Mitch McConnell (R-Ky.), 82, announced on Feb. 28 that he would step down as party leader in November. The longest-serving GOP Senate leader in history cited age as a factor.
• Feinstein, the longest-serving woman in the U.S. Senate who had a sprawling legacy, faced scrutiny over health concerns and her ability to serve during her final years in office.

By the numbers: The oldest senators are the following:

1. Sen. Chuck Grassley (R-Ia.), 90
2. Sen. Bernie Sanders (I-Vt.), 82
3. McConnell (R-Ky.), 82
4. Sen. Jim Risch (R-Idaho), 80
5. Sen. Ben Cardin (D-Md.), 80
6. Sen. Angus King (I-Maine), 79
7. Senate Majority Whip Dick Durbin (D-Ill.), 79
8. Sen. Richard Blumenthal (D-Conn.), 78
9. Sen. Ed Markey (D-Mass.), 77
10. Sen. Tom Carper (D-Del.), 77
11. Sen. Jeanne Shaheen (D-N.H.), 77
12. Sen. Mitt Romney (R-Utah), 76
13. Sen. Peter Welch (D-Vt.), 76
14. Sen. Joe Manchin (D-W. Va.), 76
15. Sen. Mazie Hirono (D-Hawaii), 76

Zoom out: There are more than 60 senators age 60 and older — that's more than half of the Senate.

• The average age of senators in the 118th Congress (which includes Feinstein) is 64 years old – unchanged from the previous class, according to data from Quorum.
• The 118th Congress is one of the oldest in U.S. history.

Zoom in: McConnell, one of the older Senators in office, had faced public pressure over his health status in the wake of several public freeze-ups.

Meanwhile, former House Speaker Nancy Pelosi (D-Calif.), 83, was among top House Democrats who stepped aside from leadership positions last year to make room for a younger generation.

• The shift had been less apparent in the Senate, particularly among Republicans.
• Still, Pelosi announced last year that she would seek another term.

Of note: The presidency is not immune from questions of fitness to serve over age, as the likeliest matchup for the 2024 election pits President Biden, who'd be 81 at the start of a second term, against former President Trump, who'd be 78.

Go deeper:

• America's aging leaders on display
• Charted: Baby Boomers rule Congress

Editor's note: This article has been updated with the latest details on the oldest senators in the Senate.