MY CHOICES FOR DEMOCRATIC PRESIDENTIAL NOMINEE

Bernie Sanders 78 in September (b September 8, 1941)
Joe Biden         77 in November (b November 20, 1942)
John Kerry       76 in December ((b December 11, 1943)
Donald Trump 73 in June (b June 14, 1946)
Eliz. Warren    70 in June (b June 22, 1949)

Because John Hickenlooper, my #3 choice, has abandoned running for president in favor of running for Senate in Colorado, I have to pick someone new.  My new choice is Democratic Gov. Steve Bullock of Montana who is 53 (b April 11, 1966) who was re-elected to the governorship with 50.2% of the vote when Donald Trump took the state with 56.2% of the vote.  No other Democratic governor accomplished such a feat.

Impressive was his defeat of Citizens Untied before the Montana Supreme Court as Montana Attorney General; however, the victory was reversed by the U.S. Supreme Court in one of the worst decisions ever made.
(https://en.wikipedia.org/wiki/Steve_Bullock_(American_politician)

I am adding some comments on Amy Klobuchar who has been av very productive Senator in the do-nothing Senate:
According to GovTrack, Klobuchar passed more legislation than any other senator by the end of the 114th Congress in late 2016.[28] According to Congress.gov, as of December 16, 2018, she had sponsored or co-sponsored 111 pieces of legislation that became law.[56] During the 115th Congress she voted in line with Trump's position on legislation 31.1% of the time.[57]
(https://en.wikipedia.org/wiki/Amy_Klobuchar)

As to Beto O'Rounke, since the El Paso shooting, he has refocussed his approach to running against Trump and is not following the early primary states.  While his new approach may bear some fruit, I'm not sure it will get him the nomination.
(https://www.nytimes.com/2019/08/15/us/politics/beto-orourke-2020-trump.html)

So my choices are:
(1) Beto O'rourke (age 46)
(2) Amy Klobuchar (age 59)
(3) Steve Bullock (age 53)

Yes, I realize that all my candidates are having trouble getting traction and are low in the polls.