NEW YORK (AP) — The age-old issue came up again recently: A potential client asked Nate Hartmann, “Hey, how old are you?”

Since Hartmann founded Yellow Box in 2010 at age 18, he’s encountered skeptics who doubted his company could design websites and create online marketing strategies. Some clients even set out to teach them.

“They tried to run us, instead of working with us to achieve their goals,” says Hartmann, whose company is based in Chicago.

Not being taken seriously is an obstacle many young entrepreneurs face. There are others, like being a boss without experience, or not understanding some legal and financial issues. But being young also has advantages. Though they may still have schoolwork to do, most owners don’t have responsibilities like families or mortgages to distract them. And they bring fresh eyes to creating products and services.

“I didn’t have preconceived notions, didn’t have any processes to shake,” Hartmann says. Many of his competitors worked at larger marketing companies, he says, and therefore “do things that aren’t efficient. But that’s what they do because they did it at the last place.”

Nearly 545,000 companies owned by people under 25 were noted in the Census Bureau’s 2012 count of established businesses, the most recent statistics available. That was 2.4 percent of all the companies in the survey. But it’s certain that thousands of other young people, including those inspired by Facebook’s launch by a 19-year-old Mark Zuckerberg, have started businesses that weren’t counted or didn’t last long.

When Tance Hughes went into business making screen-printed T-shirts and other apparel at age 17, “sometimes my age hindered my ability to secure a deal in the early days because many potential customers simply didn’t trust that I could get the job done,” he says. He sensed that people considered him not only inexperienced, but immature.

His Vidalia, Louisiana-based company, Southern Designs, did get work creating shirts for school sports teams. With momentum building, he left college after six weeks to concentrate on the business. He began to diversify his products, and transformed the company, now a decade old, into a maker of home decor including metal signs.

Although many parents support their entrepreneurial children, they can also be pessimists. Ryan Neman discovered that at age 19, when he and Skyler Lucci started HeyTutor, an online company that matches tutors with students.

“I got a lot of backlash from family and friends,” says Neman, whose business is based in Los Angeles. But he says, “I used the doubtfulness of other people to build a fire and prove them wrong.”

Neman’s father answered questions and gave advice, even as he told his son to focus on school. But Neman dropped out of the University of California, Los Angeles, in his third year.

Neman was younger than many tutors he hired. “It’s hard to interview someone who looks significantly older than you,” he says. And clients who were parents would ask, “How much trust can I offer you if you’re so young?”

Five years later, having had success, he finds more acceptance.

David Zamarin started his first company as a 15-year-old high school freshman, a shoe-cleaning business in Philadelphia whose customers included local college teams. He sold it at the end of the school year and started DetraPel, which makes a spray-on shield that repels dirt on fabric, leather and other surfaces. Zamarin, now 20 and going into his junior year at Babson College, expects DetraPel to have nearly $6 million in sales in the next year.

Having fewer responsibilities than older owners gives Zamarin the flexibility to take risks. But, he says, “you make some sacrifices. I’m in college and I don’t have a social life.”