US President Donald Trump (File Photo: CGTN)

US President Donald Trump says he feels "young" and "vibrant" at age 72 and thinks he can beat 76-year-old Joe Biden "easily."

A reporter asked Trump at the White House on Friday how old is too old to be president of the United States.

Trump said: "I just feel like a young man. I'm so young. I can't believe it. ... I'm a young, vibrant man."

Then he smiled and said he's not sure about Democratic presidential contender Biden, the second-oldest contender in the race behind Bernie Sanders.

Trump said: "I look at Joe. I don't know about him."

But he added that he would never say anyone is too old to be president.