Joe Biden is old. Really old.

If Biden wins the Democratic nomination for president and defeats President Trump in 2020, he’d be 78 years old when he moves into the White House Jan. 20, 2021.

Age has been an issue for decades, and President Reagan, then 73, handled a question about the topic beautifully when asked during a 1984 presidential debate. With Walter Mondale, 56, on stage, Reagan said: “I am not going to exploit for political purposes my opponent’s youth and inexperience.” (The debate moderator, Henry “Hank” Trewhitt of the Baltimore Sun, had a perfect response, saying, “Mr. President, I’d like to head for the fence and try to catch that one before it goes over.”)

So Biden knows the topic of his age will be front and center. On Tuesday, he was asked on MSNBC’s “Morning Joe” what he’ll do if Trump, himself 73 years old, raises the issue of Biden’s age.

TRENDING: BREAKING: Black Lives Matter Rioters in Hollywood Chase Down and Attack Driver.. UPDATE... DRIVER DETAINED BY POLICE (SHOCKING VIDEO)

“I’d say, ‘C’mon Donald, c’mon man,” Biden said, holding his hands up and waving his opponent in with his fingers. “How many push-ups do you want to do here, pal?’” Biden said. “I mean, jokingly. . . . C’mon, run with me, man.”

Biden likes to talk tough. In March 2018, the former vice president told a crowd at the University of Miami in Coral Gables, Fla., “If we were in high school, I’d take [Trump] behind the gym and beat the hell out of him.”

So it was perhaps a bit ironic when Biden said in his MSNBC interview that Trump is a “bully.”

“I’m used to bullies,” he said. “I’m used to bullies.” Then, as Uncle Joe does, he got folksy. “I remember that famous expression my grandpop used to use. They said to Harry Truman, ‘Give ’em hell, Harry,’ he said ‘I’m just gonna’ to tell the truth, they’re gonna’ to think it’s hell.’ “

I know it’ll be an ugly campaign. I know it will be not an honorable campaign that he’ll run. But I’m not backing down at all from him,” Biden said.

Still, Biden said: “I’m not gonna’ get down in the dirt with him. That’s the only place he knows how to fight.”

“But as my mother used to say, I’m not gonna’ take any guff from him.”