Kevin O'Leary: This is the biggest money mistake teens make
But Gen Z is already making money mistakes too.
"The biggest mistake teens make is the assumption that debt is free," Kevin O'Leary, financial expert and star of ABC's "Shark Tank" tells CNBC Make It.
"People use credit cards in a way that's really extraordinary. They assume that it doesn't cost anything to put anything on credit."
The truth is, however, most credit cards carry hefty interest rates if you don't pay off the balance every month. In October, CNBC reported that the average credit card interest rate spiked to 17.01 percent from 16.15 percent a year earlier and 15.22 percent two years ago.
"The fact is, the interest rates on credit cards are astronomical. The returns there are so high, even I can't make that when I invest," he says, "which is why I invest in credit card companies.
"Don't let me make money on you."
Paying so much interest "is crazy," says O'Leary.
Instead, "Don't spend more money than you bring in. Very simple concept," he says.