Americans hold $8.88 trillion of mortgage debt, according to a February report from the Federal Reserve Bank of New York. It's the largest type of household debt in the country, and it increased "substantially" during the fourth quarter of 2017 — up $139 billion, according to the report. If you're one of those millions of people with a mortgage, your top priority should be paying it off before retirement, according to Kevin O'Leary. "If you want to find financial freedom, you need to retire all debt — and yes that includes your mortgage," the personal finance author and co-host of ABC's "Shark Tank" tells CNBC Make It. You should aim to have everything paid off, from student loans to credit card debt, by age 45, O'Leary says. "The reason I say 45 is the turning point, or in your 40s, is because think about a career: Most careers start in early 20s and end in the mid-60s," O'Leary says. "So, when you're 45 years old, the game is more than half over, and you better be out of debt, because you're going to use the rest of the innings in that game to accrue capital."

Kevin O'Leary Scott Mlyn | CNBC