One Minneapolis-based millennial, who goes by the pseudonym Sean, has already managed to bank $250,000. The 28-year-old is on pace to retire comfortably by age 37.

He saves a good chunk of his $80,000 salary — more than 60 percent — which he says is doable if you focus on three expenses: housing, transportation and food. After all, as he points out on his blog, the average American spends 70 percent of their annual budget on these three expenses.

"If you can limit those expenses, that's where your big time savings will come," he tells CNBC Make It.

Here's a closer look at how he's cut back on "the big three" and how you can too: