CNBC: The 31-year-old who starting investing at 18 and is now nearly ready to retire

Did you have your finances totally figured out when you were 18?

Almost no one does. But at 18, Darren Thedieck had some ideas about where he wanted to be, and he ended up getting a few crucial things right.

Mr Thedieck started nerding out over investing in high school, reading the likes of Benjamin Graham and Warren Buffett alongside Stock Investing for Dummies. By the time he joined the Air Force in 2012 at age 18, he was determined to start investing right away.

As a result of steadily contributing to retirement and brokerage accounts over the years, the now 31-year-old has more than half a million dollars invested. He’s happy to share some of the savvy that got him there, offering a free personal finance course for fellow service members online.

“My No. 1 piece of advice would be to pay yourself first. Close your eyes and envision who you want to be in 20 or 30 years from now,” he says. “Imagine the kind of person you want to be. Imagine the things you wish you had in life. And then think about what you have to do to get there.”

How a vision for the future helps you now

Mr Thedieck’s advice echoes a sentiment frequently expressed by Buffett himself: Think about how you’d like your obituary to read, and begin building a life that lives up to it.

“I would try to think about how you’d want to look back on your life and think about yourself, and start today to go on a path that leads to that goal,” Buffett said at this year’s Berkshire Hathaway shareholder meeting.

For Mr Thedieck, who is currently stationed in Italy with his wife and daughter, the goal is a European retirement, and soon. At age 38, he’ll be eligible to retire from the military with a pension worth half his base pay.

Between his pension income and withdrawals from his investments, which he hopes to push over $1 million in the next five years, he could theoretically have enough income to fund his family’s lifestyle without pulling in a salary.

Mr Thedieck’s advice applies even if you’re not in the military or focused on early retirement. If you have a dream of owning a home or traveling the country in an RV, saving for those things should be a major line item in your budget.

“Prioritise your savings and investments for your future self just as much as you would your regular bills,” he says.

That may mean forgoing some things you want — such as fancy trips or expensive cars — in the short term, in order to put more money toward intermediate and long-term goals. That’s a far easier task if you know what the trade-off is, Mr Thedieck says.

“Start being intentional in your life with what you spend, what you save and what you do in your life, to make sure that you become the person that you want to be 20 to 30 years from now.”