Before her name was known in every American household, Martha Stewart worked on Wall Street for five years as a stockbroker. Before that, she was a model, booking clients from Unilever to Chanel.

"There were very few women at the time on Wall Street … and people talked about this glass ceiling, which I never even thought about," Stewart said in an interview for PBS's MAKERS series. "I never considered myself unequal, and I think I got a very good education being a stockbroker."

In 1972, Stewart left Wall Street to be a stay-at-home mom. A year later, she started a catering business.

At age 25, Cuban had graduated from Indiana University and had moved to Dallas. He started out as a bartender and then a salesperson for a PC software retailer. He got fired because he wanted to go close a deal rather than open a store in the morning. That helped inspire him to open his first business, MicroSolutions.

"When I got to Dallas, I was struggling — sleeping on the floor with six guys in a three-bedroom apartment," Cuban writes in his book "How to Win at the Sport of Business." "I used to drive around, look at the big houses, and imagine what it would be like to live there and use that as motivation."

Before she was Arianna Huffington, she was Arianna Stassinopolous, and at the age of 21, she met the famed British journalist Henry Bernard Levin while on a panel for a quiz show.

The two entered into a relationship, and he became her mentor while she wrote the book "The Female Woman," attacking the women's liberation movement. The book was published when she was 23.

For the next few years, Huffington traveled to music festivals around the world with Levin as he wrote for the BBC. Her relationship with Levin eventually ended because he did not want to marry or have children. Huffington moved to New York City at the age of 30. That year, her biography of Maria Callas was published, which she dedicated to Levin.

She told William Skidelsky at The Observer:

"[Levin] was my mentor. Our second date was to see 'The Mastersingers' at Covent Garden. Our first trip abroad was to Bayreuth to see 'Wagner's Ring.'"

Blankfein didn't take the typical route to finance. He actually started out as a lawyer. He got his law degree from Harvard at age 24, then took a job as an associate at law firm Donovan Leisure.

"I was as provincial as you could be, albeit from Brooklyn, the province of Brooklyn," Blankfein told William Cohen at Fortune Magazine.

At the time, he was a heavy smoker and occasional gambler. Despite the fact that he was on the partner track at the firm, he decided to switch to investment banking, joining J. Aron at the age of 27.

Rowling was 25 years old when she came up with the idea for Harry Potter during a delayed four-hour train ride in 1990.

She started writing the first book that evening, but it took her years to actually finish it. While working as a secretary for the London office of Amnesty International, Rowling was fired for daydreaming too much about Harry Potter, and her severance check would help her focus on writing for the next few years.

During these years, she got married, had a daughter, got divorced, and was diagnosed with clinical depression before finally finishing the book in 1995. It was published in 1997.

Born Shawn Carter, Jay Z grew up in a housing project in Brooklyn, New York, and became known as "Jay Z" at the age of 20. For the next few years he appeared alongside various other rappers, but "remained relatively anonymous" until he founded the record label Roc-A-Fella Records at the age of 27 with two other friends. The same year, Jay Z released his first album, "Reasonable Doubt."

He was born Ralph Lifshitz in the Bronx, New York, but changed his name at the age of 15. He went on to study business at Baruch College and served in the Army until the age of 24 when he left to work for Brooks Brothers.

At 26, Lauren decided to design a wide European-styled tie, which eventually led to an opportunity with Neiman Marcus. The next year, he launched the label "Polo."

At 24, Mayer became employee No. 20 at Google and the company's first female engineer. She remained with the company for 13 years before moving on to her current role as CEO of Yahoo.

Google didn't have the sorts of lavish campuses it does now, Mayer said in an interview with VMakers, "During my interviews, which were in April of 1999, Google was a seven-person company. I arrived and I was interviewed at a ping pong table which was also the company's conference table, and it was right when they were pitching for venture capitalist money, so actually after my interview Larry and Sergey left and took the entire office with them."

Since everyone in the office interviewed you in those days, Mayer had to come back the next day for another round.

In his early 20s, Buffett worked as an investment salesman for Buffett-Falk & Co. in Omaha before moving to New York to be a securities analyst at age 26. During that year, he started Buffett Partnership, Ltd., an investment partnership in Omaha.

New York just wasn't for him, Buffett told NBC. "In some places it's easy to lose perspective. But I think it's very easy to keep perspective in a place like Omaha."

Burns overcame a tough upbringing in a New York City housing project to get a degree in mechanical engineering from the Polytechnic Institute of NYU and then a master's from Columbia University.

Since then she's been a Xerox lifer. She started as an intern at age 22 in 1980 and joined full time a year later after getting her master's. She rose rapidly through the ranks, working in various product development roles and was named CEO in 2009.

"When I came to work at Xerox, I just chose to work. Somebody said 'how about this?' And I said OK, and I would go do that in the lab," Burns said in an interview for the PBS documentary "Makers." "Then somebody said how about doing some business planning. Then I started leaning more towards larger global systems problems. And systems problems are the business."

Zuckerberg had been hard at work on Facebook for five years by the time he hit age 25. In that year — 2009 — the company turned cash positive for the first time and hit 300 million users. He was excited at the time, but said it was just the start, writing on Facebook that "the way we think about this is that we're just getting started on our goal of connecting everyone."

The next year, he was named "Person of the Year" by Time magazine.

After graduating from the University of Virginia, Fey moved to Chicago and hung around acting workshops and even worked as the childcare registrar at a YMCA before improv troupe Second City invited her to join.

Fey told The New Yorker that she joined Second City because she "knew it was where a lot of SNL people started," and in 1997 she sent scripts to "Saturday Night Live" producer Lorne Michaels, who then hired her as a writer.

After graduating from Northern Michigan University, Schultz worked as a salesman for Xerox. His success there led a Swedish company named Hammerplast that made coffeemakers to recruit him at age 26.

While working for that company, he encountered the first Starbucks outlets in Seattle, and went on to join the company at age 29.

On his job in Xerox, Schultz writes in "Pour Your Heart Into It": "I learned more there than in college about the worlds of work and business. They trained me in sales, marketing, and presentation skills, and I walked out with a healthy sense of self-esteem. Xerox was a blue-chip pedigree company, and I got a lot of respect when I told others who my employer was ... But I can't say I ever developed a passion for word processors."

According to the Huffington Post, Winfrey was fired from the 6 p.m. news slot at Baltimore's WJZ-TV in 1977 at age 23.

In 1978, a 24-year-old Winfrey was recruited to co-host WJZ's local talk show "People Are Talking." While there, she also hosted the local version of "Dialing for Dollars."

Winfrey remained in Baltimore throughout her mid- and late-20s, until moving to Chicago in 1983 to host "A.M. Chicago" for WLS-TV.

Schmidt spent six years as a graduate student at UC Berkeley, earning a master's and Ph.D. at 27 for early work in networking computers and managing distributed software development.

He spent those summers working at the famed Xerox PARC labs, which helped create the computer workstation as we know it. There, he met the founder of Sun Microsystems, where he had his first corporate job.

In his early years as a programmer, "all of us never slept at night because computers were faster at night."

At age 25, Sandberg had graduated at the top of the economics department from Harvard, worked at the World Bank under her former professor, mentor, and future Treasury Secretary Larry Summers, and had gone back to Harvard to get her MBA, which she received in 1995.

She went on to work at McKinsey, and at age 29 was Summers' Chief of Staff when he became Bill Clinton's Treasury Secretary.

Her time at HBS was a ways before Google, but that experience helped her see the potential of the internet, she said in a commencement speech to HBS grads last year:

"It wasn't really that long ago when I was sitting where you are, but the world has changed an awful lot. My section, section B, tried to have HBS’s first online class. We had to use an AOL chat room and dial up service (your parents can explain). We had to pass out a list of screen names, because it was unthinkable to put your real name on the internet. And it never worked. It kept crashing … the world wasn't set up for 90 people to communicate at once online. But for a few brief moments though, we glimpsed the future, a future where technology would power who we are and connect us to our real colleagues, our real family, our real friends."

At age 20, Branson opened his first record shop, then a studio at 22, and launched the label at 23. By 30, his company was international.

Those early years were tough, he told Entrepreneur: "I remember them vividly. It's far more difficult being a small-business owner starting a business than it is for me with thousands of people working for us and 400 companies. Building a business from scratch is 24 hours, 7 days a week, divorces. It's difficult to hold your family life together; it's bloody hard work and only one word really matters — and that's surviving."

At age 23, Rodham Clinton began dating fellow Yale Law student Bill Clinton. She ended up staying at school an extra year to be with her boyfriend, and received a JD degree in 1973, just before turning 25. Clinton proposed marriage after graduation, but she declined.

That same year, Rodham Clinton began working at the Yale Child Study Center. Her first scholarly article, "Children Under the Law," was published in the Harvard Educational Review in late 1973, when she was 25.

After moving to Arkansas in 1975, Rodham Clinton finally agreed to marry Bill.

She'd go on to become the First Lady of Arkansas, The First Lady of the US, a US Senator, and US Secretary of State.

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