(CNN) Harry Reid, the former Senate Democratic Leader, recently remarked on the geriatric quality of his party's top tier of 2020 presidential contenders.

"We've got (Elizabeth) Warren; she'll be 71. (Joe) Biden will be 78. Bernie (Sanders) will be 79," said Reid. "It appears we're going to have an old-folks' home."

The face of the Democratic Party was considerably younger half a century ago when a 43-year John F. Kennedy beat the establishment and invented modern presidential politics.

And Kennedy's campaign started well before his 40th birthday.

"There was a conscious quest for national office that lasted five years," said Thomas Oliphant, co-author with Curtis Wilkie of a new book on the subject.

The two former Boston Globe reporters argue that JFK's campaign was much more than the year-long affair depicted in Teddy White's "The Making of the President 1960," a classic of political journalism that won the Pulitzer Prize.

"The Road to Camelot: Inside JFK's Five-Year Campaign" opens with a "cardiac double-header." In 1955, President Dwight D. Eisenhower and Senate Democratic Leader Lyndon Johnson have just suffered heart attacks when Joseph Patrick Kennedy concocts a plan. The future president's father conveys to Johnson: "With Eisenhower hospitalized, the architecture of the 1956 election has been changed. You should run for President. I will make sure your campaign never lacks for lavish financing. And my son will be your running mate."

LBJ never takes up the offer. But the 1956 Democratic convention that nominated Adlai Stevenson formally considers John F. Kennedy for VP. And even though Kennedy does not receive the nod, from that moment on, he was off and running for national office, collecting contact information on everyone who came in his orbit, setting up "Kennedy clubs," and polling public attitudes towards his Catholic faith.

Larry O'Brien, a Kennedy political strategist, is quoted in the book expressing his surprise that the Massachusetts senator was left unchallenged at the grassroots level.

"Kennedy was able to work unopposed toward the nomination for months, at least as far as grassroots American politics was concerned," O'Brien said. "The Washington columnists kept writing about what a political genius Lyndon Johnson was, and we kept locking up delegates."

"Road to Camelot" argues that Kennedy's Catholicism helped him more than it hurt him in the electoral college. It shows him playing "footsie" with southern segregationists, exchanging supportive letters with George Wallace. And it reveals that Kennedy's own polling showed that the fall debates were not what they seemed. Kennedy's polling found that while voters thought JFK looked better than the sweaty Richard Nixon -- the underlying horse race had not measurably changed from its essentially tied reality.

How LBJ got the VP job

The book offers new detail on how Johnson ended up as vice president after Kennedy clinched the nomination.

Throughout the campaign, Kennedy had operated under the assumption that Johnson would never accept being No. 2 on the ticket. The VP nomination was going to Sen. (Stuart) Symington and "then everything changed," said Wilkie. "It went haywire sometime after midnight when Kennedy was eating cereal. Dave Powers, (a Kennedy aide), got a message from Johnson saying: 'LBJ now means Let's Back Jack.'"

JFK and RFK batted around the question of whether Johnson should be on the ticket. They decided they didn't want Johnson. "The issue was trust," said Oliphant. "But still, they needed a way to placate the powerful Texan if they didn't pick him but failed to find it."

"Until a couple of year ago, I had no idea that John Kennedy rejected Lyndon Johnson barely two hours before he picked him as his running mate," said Oliphant. "These bits of history are hardly deep, dark secrets. They have been hiding in plain sight for decades -- mostly at the Kennedy Presidential Library."

"But a lot of this stuff has barely been looked at," Oliphant added.