A senator/governor born 1970 or later will mostly likely be President in 2024...

[mencken]

Let's consider where the recent nominees have been 9 years prior to the election:

Mitt Romney	2003: Newly-elected Governor of Massachusetts
Barack Obama	1999: State senator
John McCain	1999: Arizona Senator; running for President
John Kerry	1995: Massachusetts Senator
George W. Bush	1991: son of President
Al Gore	1991: Tennessee Senator; failed Presidential candidate
Bob Dole	1987: Senate Minority Leader; running for President
Bill Clinton	1983: Governor of Arkansas
George Bush	1979: Former CIA director; running for President
Mike Dukakis	1979: Former Governor of Massachusetts

So yes, it does seem that it is likely that the 2024 winner would be one of the names you spot if you took a sieve of all the current Senators and Governors that would be within a plausible age range (Just a coincidence that the only three "unknowns" on that list ended up winning it all). Further, there is a good possibility that the 2024 winner is a candidate for President right now; or would be running for President if Hillary were not.

[mencken]

Let's consider where the recent nominees have been 9 years prior to the election:

Mitt Romney	2003: Newly-elected Governor of Massachusetts
Barack Obama	1999: State senator
John McCain	1999: Arizona Senator; running for President
John Kerry	1995: Massachusetts Senator
George W. Bush	1991: son of President
Al Gore	1991: Tennessee Senator; failed Presidential candidate
Bob Dole	1987: Senate Minority Leader; running for President
Bill Clinton	1983: Governor of Arkansas
George Bush	1979: Former CIA director; running for President
Mike Dukakis	1979: Former Governor of Massachusetts

So yes, it does seem that it is likely that the 2024 winner would be one of the names you spot if you took a sieve of all the current Senators and Governors that would be within a plausible age range (Just a coincidence that the only three "unknowns" on that list ended up winning it all). Further, there is a good possibility that the 2024 winner is a candidate for President right now; or would be running for President if Hillary were not.

It's also worth noting that many of the last elections have been won by the candidate who entered major office last.

That's been the case in 1992, 1996, 2000, 2004, 2008 and 2012.

Also based on that list, the median half of ages were between 45 and 56. Thus, I think the criterion should be expanded to include names born after 1959. Expanding this criteria adds notable individuals such as Booker, Gillibrand, Baldwin, Klobuchar, and Bullock for the Democrats and Walker, Ducey, Sandoval, Christie, Martinez, Pence, Ayotte, Tim Scott, Paul, Flake, and Thune for the Republicans.

[mencken]

If Hillary is elected, the ages of presidents post-primary reform: 52, 69, 64, 46, 54, 47, 69. More over 60 than under 50. So who knows?

A bit presumptuous, considering two of the three most likely Republican candidates are under 50.