Donald Trump, born in 1946 (the same year as Bill Clinton and George W. Bush), was the oldest president ever to be inaugurated -- but it's looking like his nominal challenger this year will be even older, either Joe Biden (b. 1942) or Bernie Sanders (b. 1941). Not that either of them has a cat in hell's chance of winning.
Though there have been two presidents born in 1924 (Jimmy Carter and Bush père) and three born in 1946, not a single person born in the 21 years between those two dates has ever been elected president. Of the 12 generations (as identified by Strauss and Howe) from George Washington to Barack Obama, every one has produced presidents with the single exception of the "Silent Generation" of Biden and Sanders.
The graph below shows, for each Strauss-Howe generation, how many years it held the presidency vs. how many years of birth the generation spans. For example, Strauss and Howe define the Greatest Generation (actually they call it the "G.I. Generation") as those born in a 24-year period (1901-1924), but members of that generation held the presidency from Kennedy to Bush père, for a total of 32 years, for a ratio of 32:24 or 1.33. (The graph assumes that Trump will be reelected, giving the Boomers -- actually, giving people born in 1946 -- 24 years in office.)
Why did the presidency skip that entire generation? I have no idea. There is a similar gap in British PM birth years between Margaret Thatcher (b. 1925) and John Major (b. 1943), though Mrs. Thatcher does just barely qualify as a member of the Silent Generation according to Strauss and Howe's dates. However, Silents dominated the U.S. Senate for just as long as any other generation, so it's not as if there was a shortage of political talent.
