The things that hurt Jerry Brown back then were his New Age-ish image. The Governor Moonbeam thing. Having Linda Ronstadt as his girlfriend. These things wouldn't hurt him today, but back then, when he was young, this detracted from the fact that he was a serious public official.
I can't imagine what a "younger Jerry Brown" would be like today, because I am well acquainted with what the real "younger Jerry Brown" was. He would be somewhat less in demand as a Presidential candidate because California is now like Massachusetts in terms of voting Democratic for President, something that was NOT true when Brown was younger. The Jerry Brown of 1976, for better or worse, stood out from the rest of the Democratic field by advocating new ways of looking at things that were considered trendy because of the weariness even Democrats had with the Great Society. He was a neo-liberal, for better or worse, and that stood him apart from both the traditional liberals and the Southern moderates. Today, he doesn't really stand out from the crowd, and I don't see how there would be a demand created for a candidate like him when there are a whole lot of candidates like him today.
I meant some vita like this without his previous tenure as governor:
Born in 1953.
1991-1999 California Secretary of State
1999-2007 Mayor of Oakland
2007-2011 California Attorney General
2011-2019 Governor of California
Jerry Brown is intriguing and impressive specifically because of his previous term as California Governor and his three (3) runs for President. The hypothetical Jerry Brown presented here isn't anything special.
A Brown born in 1953, assuming he had the same leg up from his father having been governor, could have previously been governor from, say, 1987 to 1995, and run for president in 1992 and 1996.
A 34 year old governor and 39 year old presidential candidate? That would have been an awful accelerated timeline
He was only 36 when he first became Governor and 38 when he first became a Presidential candidate.