As always, why?
In October 2017, Feinstein declared her intention to run for reelection in 2018. She lost the endorsement of the California Democratic Party's executive board, which opted to support State Senator Kevin de León, but finished first in the state's "jungle primary" and was reelected in the November 6 general election.
https://en.wikipedia.org/wiki/Dianne_Feinstein#Elections
Feinstein won 54% of the general election vote. Californians are, by and large, apparently not too concerned about advanced age as a disqualifier. If they don't see the need, why should you or anyone else seek to impose it on them with a law?
(There's the party doing what some people think it should have done, by the way.)