Story highlights Ben Carson reveals he wasn't always soft-spoken

Comments come after Donald Trump criticized his low energy level

Washington (CNN) Ben Carson says he's soft-spoken now -- but he hasn't always been so calm.

"As a teenager, I would go after people with rocks, and bricks, and baseball bats, and hammers. And, of course, many people know the story when I was 14 and I tried to stab someone," Carson said Sunday on NBC's "Meet the Press."

"You know, fortunately, you know, my life has been changed," he added. "And I'm a very different person now."

Carson's comments came after Donald Trump, his leading opponent for the Republican presidential nomination, said at a rally in Miami on Friday that Carson has even less energy than Jeb Bush, who the developer has repeatedly called a "low-energy" candidate.

"Ben Carson is super low energy, right? He's super low," Trump said. "Super low energy. We need tremendous energy. We need tremendous energy."

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