Much of the polemic supporting Hillary Clinton for president focuses on how qualified her experience makes her. I wish there would be less emphasis on that. It's a point, yes, but not a very strong one. What matters is what's been done with that experience, and while Clinton's abilities and policies can be robustly defended, dispute over that is what the argument over her is about.
Experience alone doesn't qualify. The most broadly and lengthily experienced president in US history was James Buchanan, also the worst president in US history; and Obama was elected for his judgment and gravitas, despite a notable lack of experience. Indeed, some pointed out at the time that Obama's resume - a lawyer from Illinois with a certain amount of state legislative experience and a couple years in Congress - was not as thin as it sounded. We'd once previously elected a president with that resume, and he'd turned out to be pretty good.
More seriously, I'm reluctant to go back as far as Lincoln to draw comparisons, since the duties of both President and other offices has changed so much since then, but it might be useful to compare post-WW2 presidential nominees in simple cumulative time of relevant experience. The question is, what counts as relevant experience? Of course a wide variety of personal experiences, including in business, can help prepare a candidate, but I'm going to focus mostly on high government office, though noting other leadership positions.
1948, Truman v. Dewey. Truman had already been president for almost four years, of course, and there's no preparation for the presidency like being president, but it's worth noting for comparative purposes that he'd previously been senator and vice president for 10 years, and that his 8 years as chief executive of his county might also be relevant. Dewey had at this point been governor for 6 years, and before that had been a leading prosecutor for about another 6 years.
1952, Eisenhower v. Stevenson. Eisenhower was nominated for his generalship, and he'd been a commanding general for a total of 6 years, starting with his appointment to Operation Torch, up through his time at NATO. He'd also been president of Columbia University for about 4 years. Stevenson had been governor of Illinois for 4 years.
1956, Eisenhower v. Stevenson. By this time Eisenhower had 4 years as president, while Stevenson hadn't done much during the same time except campaign, as far as I can tell.
1960, Kennedy v. Nixon. Kennedy, 14 years in Congress (both houses). Nixon had spent the same 14 years with 6 in Congress and 8 as VP.
1964, Johnson v. Goldwater. Johnson had nearly 24 years in Congress and 3 as VP. Goldwater had been a senator 12 years. He'd been running the family business for over 20 years before then, though.
1968, Nixon v. Humphrey. Governmentally, Nixon was still the same 14-year man he'd been in 1960. Humphrey had been a big-city mayor for 3.5 years, a senator for 16 years, and VP for 4, totaling 23.5.
1972, Nixon v. McGovern. Nixon was now incumbent. McGovern had served in Congress for 14 years and had been director of a big federal program for 1.5.
1976, Carter v. Ford. Carter had been governor for 4 years and previously in his state legislature for 4. He'd also, like Goldwater, been running his family business for over 20 years. Ford, before becoming president 2.5 years earlier, had been in Congress for 25 years and VP for over .5.
1980, Reagan v. Carter. Reagan had been governor for 8 years. I'm not sure whether to count his almost 6 years as president of the Screen Actors Guild.
1984, Reagan v. Mondale. Mondale had been a senator for 12 years and VP for 4, plus his state's attorney general for 4.5, making 20.5.
1988, Bush v. Dukakis. Poppy Bush may have been the first modern candidate to run on his resume. He'd been in Congress for 4 years, an ambassador (under varying titles) for 3, a cabinet-level executive for 1, and VP for 8, totaling 16. Previously, he'd been active as an oil executive for about 12 years. Dukakis had been governor for 12 years and in his state legislature for another 8.
1992, Clinton v. Bush. Clinton had been governor for 12 years and his state's attorney general for 2.
1996, Clinton v. Dole. Dole had served in Congress for an awesome 35.5 years before resigning during his campaign, and previously in his state legislature for 2.
2000, Bush v. Gore. Bush had been governor for 6 years; he also spent 5 years as managing general partner of a baseball team. Gore was in Congress for 16 and VP for 8, totaling 24.
2004, Bush v. Kerry. Kerry had been a senator for 20 years and previously lieutenant governor for 2.
2008, Obama v. McCain. Obama, 4 years in the Senate and 8 in the state legislature. McCain, 26 in Congress.
2012, Obama v. Romney. Romney was 4 years as governor, the least governmental experience of any candidate since Stevenson. But he spent 3 years running the Salt Lake Olympics, plus approx. 15 years at Bain Capital.
2016, Clinton v. Trump. Clinton has been a senator for 8 years and Secretary of State for 4, making 12; add in 8 years as an activist First Lady and that makes 20; if her 12 years as First Lady of Arkansas also count, it comes to 32, the highest figure yet on this list except for Dole. If business counts, however, Trump seems to have been in charge of his own businesses for 45 years now, so he's either the lowest or the highest.
So we get, counting first runs for president only, governmental and military command only and giving two figures where questionable:
37.5 Dole (high)
35.5 Dole (low)
32 Hillary Clinton (high)
24 Truman (high), Gore
22 Kerry (high)
20 Dukakis (high), Kerry (low), Hillary Clinton (low)
16 Poppy Bush
14 Truman (low), Kennedy, Nixon, Reagan (high), Bill Clinton
12 Dewey (high), Goldwater [also in business], Dukakis (low), Obama (high)
10 Eisenhower (high)
8 Carter (high) [also in business], Reagan (low)
6 Dewey (low), Eisenhower (low), W. [also in business]
4 Stevenson, Carter (low), Obama (low), Romney [also in business]
0 Trump [also in business]