Most people don't start saving for retirement until they land their first "real" job as a 20-something. Even then, they're often lazy about setting up their 401(k) and putting any extra cash away with consistency.

But the story is different for the Money Wizard, a 26-year-old financial analyst and blogger with a six-figure net worth who started saving before he could even get behind the wheel of a car.

"I remember my eighth-grade math teacher posed the magical doubling penny question to us, which opened my mind to the power of compound interest," the Money Wizard — who goes by the pen name Sean online — told Business Insider.

"I still remember his exact quote," he said. "'Instead of buying a few CDs with your money, you could be a millionaire.'"

A few years later, Sean realized that his grandfather, "one of the cheapest guys" he knew, was actually a millionaire. "He never made more than a low five-figure, blue-collar salary, but he used the stock market to save his way to $1.2 million in investments" by age 60, Sean said.

Inspired by his grandfather's financial finesse, he started saving any extra cash he earned from his first job at age 16. Later, after reading a book called "Early Retirement Extreme" by Jacob Lund Fisker, he became determined to reach financial independence by age 37.

At 22, he graduated college with a degree in finance and economics and got hired as a financial analyst in Denver making $45,000 a year. He immediately set up his employer-sponsored 401(k) and contributed 5% of his pretax salary, which was fully matched by the company.

Now, three and a half years later, Sean's salary is $70,000 and his 401(k) contribution — just one of his vehicles for saving — is up to 25%.

Last year, at age 25, his net worth reached $100,000. That's when he started his blog, My Money Wizard, to share his ambitious journey to early retirement.

As of August 2016, Sean's net worth was nearly $150,000. Below, he talks us through the growth of his savings accounts and why each is vital to achieving his goal of retiring before 40.

Although Sean requested anonymity, Business Insider reviewed tax and bank statements that confirmed the figures he's reported.