Reining, who is based in Madison, Wisc., wanted something different , he says: "The freedom to do what I want to do when I want to do it. And that's when I first made that shift from spending all this money on stuff that really wasn't making me any happier, to saving and investing it."

"By my late 20s, I had bought a condo, I had bought a BMW and I'd go to Whole Foods every week," the now 38-year-old tells CNBC. "I was living a pretty good lifestyle. But in my late 20s, I started becoming a little disillusioned with the whole 9-to-5 grind."

Chris Reining landed his dream job in IT out of college . It came with a nice salary, which made possible a nice lifestyle.

He worked his way up to saving 54 percent of his income and focused on increasing his revenue streams, which allowed him to build a $1 million portfolio by age 35. Two years later, Reining officially retired.

The key to saving more than half your income, he tells CNBC, is to start with small changes: "I know there are some people out there that say you shouldn't worry about the $5 latte, but the more I think about it, cutting out the $5 latte was a good place to start. Because if you try to downsize your house, get rid of all yours cars and make all of these drastic changes, it's so overwhelming and you're not going to do any of it."

After cutting out his morning coffee, Reining eliminated the $15 lunches he bought every day. Next, he cut out the bigger things, such as the $1,000 a month he spent flying airplanes.

"The small changes will lead you to be able to make the big changes," Reining says. Plus, "you can always go back and add the small changes in later.

"Now I buy a $5 latte and it's no big deal, but I think it was really important to get the ball rolling by starting with something small."

Don't miss: 38-year-old retired millionaire: One simple habit leads to wealth