The romanticized image of the symphony orchestra conductor - arriving by limo at a grand music hall to inspire effortless beauty before thousands - is a world away from young Geoff McDonald's catch-as-catch-can career.

Example: Driving to a recent conducting audition with the Philadelphia Youth Orchestra, he was pulled over because the registration for the car he'd borrowed from his sister had expired. So instead of focusing on the audition piece, Beethoven's lofty Symphony No. 9, he was muttering choice words about his sister as the minutes ticked away.

Arriving at the rehearsal hall barely in time, he hoped he wouldn't be asked to conduct the symphony's third movement, the most sublime - and the toughest to sustain.

But after a quick huddle with Louis Scaglione, the youth orchestra's formidable music director, McDonald set his jaw, headed for the podium, and held up three fingers. Yes, the third.

Within a few weeks, he had the job.

Only a fellow conductor can fully appreciate what that meant: At 25, the native Philadelphian would be conducting, rather than simply observing at the feet of one maestro or another.

This may be the Age of the Young Conductor - the domination of older talents is being eroded by, among others, Gustavo Dudamel, now 29, in Los Angeles and Yannick Nézet-Séguin, 35, in Philadelphia - but most newcomers still start more or less at sea. The Philadelphia Youth Orchestra just might be McDonald's life raft.

"There's no real track for conductors," he said. "Nobody seems to know how this works. Part of my anxiety is that I have no idea what constitutes a foothold."

In his newest gig, McDonald will work chiefly with the Young Artists Orchestra, an ensemble of gifted players ages 8 to 21 that feeds into the Philadelphia Youth Orchestra. The PYO is one of the best of its kind - and one whose culture he knows well, having been a cellist in the group. That's partly what got him the audition.

"He understands our teaching philosophies because he was part of that rigor," Scaglione says. "It saves a lot of time in training a new assistant. He has confidence when he steps on the podium. He managed the rehearsal efficiently and proficiently."

The orchestra's programs are standard repertoire, which McDonald needs to help stabilize other elements of his piecemeal existence. As assistant conductor with the American Symphony Orchestra at the Bard Festival, he backs up chief conductor Leon Botstein (who never gets sick) by learning fringe repertoire that might not come in handy for years. He's also part of the incidental music team for the New York revival of Angels in America, but as an assistant to composer Michael Friedman. As the New Amsterdam Singers' assistant conductor, he leads one piece per concert.

It's hard to know how, or if, it will all add up.

McDonald is loaded with promise, as well as with degrees from Princeton University and the Mannes College of Music, from which he graduated in 2009. But the period between graduation and the first big job can be horrific. Even Leonard Bernstein had a barren summer in the early 1940s that haunted him to the end of his days.

Few professions are as glamorous and artistically fulfilling as conducting - but only for a select few. Many others labor quietly in semipro orchestras or educational institutions. And far more sink into complete obscurity; a young conductor can land a prestigious master class with a titan of the podium, yet never be heard from again.

"It truly seems that almost anything could be 'the thing' that opens up a great opportunity down the road," McDonald says.

So many members of the New Amsterdam Singers have raved to founder/director Clara Longstreth about McDonald that "I could be threatened, but I'm not," she says. He has the X-factor that makes musicians eager to give their best - and, she adds, his good looks don't hurt.

Nobody yet calls him "maestro," but one of the singers, New York Philharmonic publications editor Lucy Kraus, calls him "a major talent."

An unexpected plus is McDonald's role as cellist in an indie-rock band that started in his Princeton years - Miracles of Modern Science, a string trio plus drummer and mandolin. In the past, conductors (Andre Previn, for one) needed decades to live down a nonclassical past. But when she was sifting through 64 applications for the New Amsterdam job, Longstreth found McDonald's rock credit "bizarre and interesting . . . it told me he has lots of interests. That's great."

"He's one of my favorite students," said David Hayes, conductor of the Philadelphia Singers and teacher at Mannes. "He has this voracious inquisitiveness. . . . You mention something that he doesn't know, or open a small door that might lead to an area of investigation, and he takes off after it. . . .

"My advice to him: Don't turn down anything."

Yet a seemingly good staff conducting position with a major orchestra might yield only family concerts - and little chance of advancement. At the same time, the limelight can be unhealthy. One of McDonald's Mannes buddies, Francesco Lecce-Chong, commuted last month between Philadelphia (where he's a Curtis Institute student) and the small-scale Brooklyn Repertory Opera to conduct Strauss' Die Fledermaus. He was happy to be under the radar.

"Without outside pressures of large-scale fund-raising and reviews, I can be comfortable trying everything I know," he wrote in an e-mail. "Musicians and singers in these groups are also very flexible when I need to rethink and change things."

The art itself seems invisible: Conducting involves no physical contact with a musical instrument. It is said that conductors "play" an orchestra, but there's no way to practice in domestic privacy. In effect, conductors always play on a borrowed instrument.

And success is often a matter of alchemy. Philadelphia legend Eugene Ormandy's inability to manage complex time signatures might have barred him from a major career today. Yet in his time, he achieved results by projecting complete authority, without which even well-equipped conductors might fail to impress musicians, leading to telepathic wars of the wills.

So why would any sensible person want to conduct?

For McDonald, the decision evolved during his suburban upbringing and his time at the Haverford School: "I found that I had an opinion or point of view about the performance long before I knew how to articulate what was right or wrong."

Though he started piano at 5 and cello at 10, and sang in choirs along the way - all aided by the gift of perfect pitch - he hated the long, lonely practice hours.

"I was happier collaborating," he says, "and excited by all the nerdy things that music theory had to offer. I had wonderful support of teachers, and all of the sudden, they were saying, 'You should become a conductor.' "

By age 15, he had given up hockey to protect his hands and was conducting school groups. His parents - a lawyer and a marketing consultant, both musically inclined - were encouraging.

McDonald's interest in the humanities directed him not to a conservatory but to Princeton, where the University Symphony Orchestra was there for the conducting. After graduating in 2007, he auditioned at Philadelphia's Curtis Institute of Music and made it to the final round, but was happy to land instead at Mannes, where technique was drilled into him "without shattering my confidence."

Now, his conducting manner can turn on a dime. For choral groups, his batonless hands are fluid, almost balletic; for Beethoven, the baton is wielded. When the music-making goes awry, he'll flash a smile at the offending section, which somehow corrects the problem immediately. He doesn't confront difficulties as much as circumvent them with strategy. "You won't go flat if you're thinking through the entire phrase," he told the New Amsterdam Singers at one recent rehearsal.

If such strategies don't work on the Philadelphia Young Artists Orchestra, can McDonald manage a mighty harangue? Without hesitation, he says, "Yes."

Hayes isn't surprised: "Underneath that veneer of civilization, he has a very strong personality. . . . He was relentless in going after what he wanted."

He'll have to be, given his stated specialty: Gustav Mahler, the great Austrian Jewish composer of vast, tortured symphonies into which many claim to have special insights.

"But I mean it more than everybody else," he says. "Mahler has been the reference point for everything I've done. Whenever I learn a new idea . . . I bring it back to Mahler. That's the proving ground for any idea I might have."

How can someone McDonald's age connect with the existential hopelessness of Mahler's Kindertotenlieder ("Songs on the Death of Children"), which he has conducted? "I've always had a crippling self-doubt," he says, "enabled by a healthy dose of Jewish neurosis, my last name notwithstanding."

At this point, his best chance for conducting repertoire of his choice is to form his own orchestra, a not-implausible scenario; he talks about organizing something small-scale with Mannes friends. He also thinks about moving to Europe, where classical music is not a second language and orchestras are seemingly everywhere.

And what about Miracles of Modern Science? Already on YouTube (try "Eating Me Alive"), the group has been working feverishly in a cramped Brooklyn studio on its second album. Live engagements have included such high-end venues as Manhattan's La Poisson Rouge.

"We've got a good 50 minutes' worth of quirky, catchy pop tunes," McDonald says. "If the band takes off, then I'll have some difficult decisions to make. Is there a plan? I'm just throwing the pieces up in the air to see where they land. This is the way my musical life has always been - a mosaic of impulses.

"But," he adds, "when I wake up in the morning, I'm a conducting animal."