Washington venerates its ancients, idealizing and idolizing the elder statesman, lavishing perks and institutional potency as rewards for seniority.

Yet the city also runs on the fuel of youth, the recent college grads who staff the offices, and the rising professionals whose ambitions juice the city’s striver culture.

In the fuzzy middle between those poles lie the 50-somethings, federal Washington’s version of tweeners, a demographic group fraught with generation-straddling, career-tweaking, life-altering conundrums: Dump that modest-paying but idealistic government gig for private-sector riches? Hang in there for one more term in hopes that a committee chairmanship finally will be yours?

On Thursday, President Obama — one of American history’s most precocious achievers — joins the ranks of Washington 50-somethings, an age span he’ll share with 29 U.S. senators but just one of 16 Senate committee chairmen (that would be Mary Landrieu, the Louisiana Democrat who sits atop the Small Business and Entrepreneurship Committee). Reaching the pinnacle of American power so early means Obama will have to figure out what to do with himself for a big chunk of his 50s, whether in 2013, when he could become a 51-year-old one-termer, or in 2017, when he could leave office as a 55-year-old two-termer.

Obama will become just the third president to turn 50 in office in more than 130 years, following Theodore Roosevelt, whose low-key 50th in 1908 prompted a stream of messenger boys delivering congratulatory notes to the White House, and Bill Clinton, who celebrated hitting the mid-century mark in 1996 with a star-studded party and fundraiser.

As Obama’s 50th approaches, he’s taken to quipping about getting grayer, but he still gets up and down a basketball court without reaching for the oxygen tank. Obama celebrated his 49th last year by dining with Oprah Winfrey and a few other friends while his wife and kids were vacationing. This year, he’s expected to do it up big, with a party in Chicago featuring Jennifer Hudson and Herbie Hancock, and a $35,800-a-head fundraiser.

On the occasion of Obama’s 50th, five prominent Washingtonians — uber-pundit Paul Begala, lobbyist Scott Reed, former White House press secretary Joe Lockhart, Rep. Mike Quigley (D-Ill.) and Labor Secretary Hilda L. Solis — agreed to help unpack what it means to reach that milestone in the nation’s capital, a city with a culture like none other in the United States.

The group includes one person who joined Washington’s tweener cadre in each of the past five years. A common thread, expressed in varying forms, emerged from these conversations: Washington functions as a transient city given to a permanent obsession with who’s up and who’s down, who merits being kowtowed to and who will be doing the kowtowing. And the 50s is the decade when the city often measures whether you’re a player with true staying power or just another so-and-so passing through.

A Washington 50-something

We “don’t quite fit the world of the senior statesman, like a Lee Hamilton or Warren Rudman or Robert Gates,” Lockhart says one afternoon.

But “most people in their 50s, they’re not necessarily going to work on the Hill or at the White House,” adds Lockhart, who was born in 1959 and turned 50 in 2009.

By 50, the archetypal Washingtonian power players have done all that. They may have punched their tickets working low-level jobs in campaigns (then less-low-level, then high-level), served a president or a senator or two, then gotten themselves an undersecretary or senior adviser slot or gotten elected to Congress.

Take the Class of 1957 babies, for instance. Margaret Spellings became domestic policy adviser to President George W. Bush in her late 40s, crossed over into her 50s as secretary of education, and finished her term in the Cabinet with most of her 50s still ahead of her to morph into a sought-after education consultant. David Addington went from Vice President Dick Cheney’s inner circle to a lofty perch at the Heritage Foundation. Terry MacAuliffe traipsed from super-size fundraising for President Bill Clinton to a failed run for Virginia governor and a series of mega-buck business adventures.

Congress is crawling with 50-somethings. In the House of Representatives, 137 members are in their 50s, a hair more than 60-somethings, of which there are 129. The House 50-somethings range from Arkansas Democrat Mike Ross, who just turned 50 on Tuesday, to New Hampshire Republican Charles F. Bass, who’s got just six months of his 50s left.

“I’m sort of in the middle,” says Quigley, who was born in 1958 and turned 50 in 2008. Not a congressional youngster, but not yet part of the senior statesmen club.

Quigley, who stays in shape by playing hockey twice a week and encourages Obama to keep playing basketball, reasons that respect on the Hill comes from being seen as someone who will dig deeply into issues and work. Few could question Quigley’s commitment to the place — he sleeps in his office rather than renting an apartment. “I’d like to think that I’ve started to earn their respect,” he says of his older colleagues.

The risks and rewards of Washington give an element of high-stakes intrigue to the have-you-made-it question. A case in point: the mega-lobbyists in the Class of 1958 babies. Jack Abramoff, ex-con; Ed Rogers, a go-to guy for Republicans.

“We keep score differently,” says Lockhart.

Washington math goes something like this: the number of powerful people you can get on the phone plus the number of people who think you can get those powerful people on the phone. By the time you’re 50, that had better be a big number.

Wall Streeters in New York might compare the girth of their wallets or the square footage of their weekend homes in the Hamptons, but “D.C.’s more about the power you’ve accumulated,” says Lockhart, who recently left the hugely successful strategic communications firm he co-founded for a hugely important worldwide communications job with Facebook, based in its Washington office. “Have you been at the center of this issue? Did you drive the discussion?”

Reed, the Washington institution who managed the 1996 presidential campaign of then-Sen. Bob Dole (R-Kan.) and now runs a lobbying shop, expands the definition further. “In this town, it’s power, access, knowledge,” says Reed, who was born in 1960 and turned 50 last year. “It’s a different model.”

That’s not to say money doesn’t matter here. When Washington power players are in their 40s, conversations with their peers often veer to chatter about their kids’ soccer games, Lockhart says. In their 50s, the conversation is about paying for college. “It’s a period when people concentrate on themselves, as opposed to their candidates or their issues,” he says.

Naturally, Reed’s 50th arrived with a demonstration of his big-man-in-town status. Reed’s girlfriend threw a huge surprise party for him. Boardroom big shots from across the country and inside-the-Beltway muscle toasted him into Washington’s tweener decade, an outpouring of friendship that suggested a lot of people are betting Reed will be worth knowing for a long, long time. At 50, his Washington math added up.

“If you’d lined up all the private planes at Dulles, it probably could have been an air force for a small South American country,” Reed deadpans.

In other professions — in other towns — 50 might be a little late for your peers to declare that you’ve arrived, but not in Washington. The city, of course, has its baby-faced stars, but it remains a capital of reverence for paying dues, checking off boxes marked “undersecretary” or “assistant” such-and-such.

“People spend a lot of time working their way up. It takes longer to get good at politics,” says Begala, a former top adviser to Clinton who has become one of the nation’s most recognizable political pundits. “It’s different than L.A., where youth is everything, or New York with the young turks. Or sports.”

No longer a kid in the room

At some point, it dawns on the Washington 50-something: He (or she) is no longer the youngest person in the room. You’re special when you’re the young one who pushes your way into the war room with the “senior” staff. You’re the “comer,” the “go-getter,” the “young woman to watch,” the “young guy with a bright future ahead of him.” The city, for all its commitment to seasoning, also loves the idea of potential.

“You were always the youngest this, the youngest that,” says Begala, who was born in 1961 and turned 50 in May. “When you’re 50, that’s totally untrue.”

He feels it when he’s hanging around with other central players at Priorities USA, a political action committee he’s involved in. He’s the “old guy” in the room, so when he makes “some reference about the ’70s or ’80s,” they tease him about having a “rotary cellphone.” Begala embraces it, perhaps taking a cue from his old boss. After Clinton turned 50, Begala recalls the stock response when people at the White House asked the president how he was doing: “Not bad for an old man,” Clinton always said.

Obama is the first president younger than Begala, the pundit notes. “If I’m ever older than the pope, then I’ll know I’m dead,” he says.

There’s another thing about no longer being the kid in the room, says Lockhart, who is surrounded by a much younger crowd at Facebook: “People actually expect you to know something.”

But what happens when the lines aren’t so clear? What happens when people aren’t quite sure whether to afford you the “Yes, ma’am” or the “Yo, girlfriend” treatment?

Then you’re truly in that fuzzy space occupied by the Washington 50-something, the politico-celestial orbit traveled by Solis, Obama’s youthful-looking secretary of labor.

“I’ve been in meetings where people call me ‘dear,’ ” says Solis, who was born in 1957 and turned 50 in 2007. “On the one hand, I don’t want to be thought of as very old; on the other hand, I don’t want to be underestimated.”

Solis routed to Washington through the California legislature, where she was one of the youngest elected officials in the state. The old lions in Sacramento took to her, in part, because she was respectful, forming something akin to a “father-daughter” bond that served her and her constituents well, she says. But now, having become the first Latina Cabinet member in U.S. history, she’s sought to find a balance between the honorifics that come with Washington power and the vibe that makes her comfortable.

For instance, she’s not a fan of being addressed as “madam secretary,” the standard protocol for Cabinet secretaries. “Hilda” is just fine by her, she says on the phone one afternoon. Then she pauses. She seems to be searching for the right way to express what’s on her mind.

An aide listening in on the conversation interjects. “I’m going to say it,” the aide says. “Makes you sound old.”

It’s ‘about surviving’

One night after the 2000 congressional election, Quigley — the Illinois congressman who was then a member of the Cook County Board of Commissioners — had dinner with a 39-year-old aspiring politician who had just been trounced by a 50-something incumbent congressman. The losing candidate’s name was Barack Obama.

Obama confided that his wife, Michelle, thought that maybe he should sit out the next election, Quigley recalls. The future seemed uncertain, but Quigley was reassuring.

“There’ll be something for you,” Quigley told the future president of the United States.

It was a small piece of advice, but it illustrated a fundamental about politics that translates to Washington. Sometimes it’s just about staying in the game. Administrations come and go. Republican dominance will be declared, then Democratic dominance, then Republican, then Democratic.

“A big part of Washington is about surviving,” says Reed, the lobbyist who is also an avid boater. “The tide comes in twice a day on the Potomac — and lots of people get washed away.”

On turning 50, Reed took a moment to reflect. He realized that he’d been surviving — no, thriving — in this town for 30 years and that he’d made a lot of friends. And, he thought to himself, he’ll probably be here 30 more.

Staff researcher Madonna Lebling contributed to this report.