How many senators served until they were at least 90?

[Southern Senator North Carolina Yankee]

Too many. 80 should be mandatory retirement age

The Senate is suppose to be full of old people.

The old people that are suppose to kick the popular majority in the house in the nuts when they go too far. Of course the house doesn't work like that because of gerrymandering and too few districts, and since many Senators are sourced from the House, well you can guess the impact on the Senate.