"But I think that's true for multiple other people that would want to run," the Florida Republican tells Jonathan Karl. "I mean I'll be 43 this month, but the other thing that perhaps people don't realize, I've served now in public office for the better part of 14 years."
Rubio stressed the Republican Party has several viable candidates.
This week on CloseUP, Josh McElveen sits down with Florida Sen. Marco Rubio.
"The question is … who's vision is the one that our party wants to follow?" Rubio says.
On that point, Rubio says, "Most importantly, I think a president has to have a clear vision of where the country needs to go and clear ideas about how to get it there."
Karl twice put the question to Rubio: You think you're ready to be president?
"I do," Rubio replied both times.
Karl talked to Rubio in Manchester, N.H., and the senator repeated that he will decide whether to run for the White House by year's end. If he runs for president, he will take an all-or-nothing approach.
"If I decide to run for president, I will not have some sort of exit strategy to run for the Senate," Rubio said. "I believe that if you want to be president of the United States, you run for president."
Rubio gives Hillary Clinton, the Democratic front-runner for president, an F for her time as secretary of state.
"If you look at the diplomacy that was pursued in her time in the State Department, it has failed everywhere in the world," Rubio said. "So here's what I would say, if she is going to run on her record as secretary of state, she is also going to have to answer for its massive failures."
Those failures, he said, include a reset with Russia and the Benghazi attacks.
On climate change, Rubio said he doesn't buy that mankind is adding to the problem.
"I don't agree with the notion that some are putting out there, including scientists, that somehow there are actions we can take today that would actually have an impact on what's happening in our climate," Rubio says. "Our climate is always changing. And what they have chosen to do is take a handful of decades of research and say that this is now evidence of a longer-term trend that's directly and almost solely attributable to man-made activity, I do not agree with that."