NEW YORK (Reuters) - Warren Buffett told investors on Saturday that Berkshire Hathaway Inc, which he has run for 50 years, has found his successor, giving more details than he ever has about the selection.

"Both the board and I believe we now have the right person to succeed me as CEO - a successor ready to assume the job the day after I die or step down," the billionaire said in his annual letter to Berkshire shareholders.

"In certain important respects, this person will do a better job than I am doing," he added.

Buffett also strongly suggested that the person already works within Berkshire. "Our directors believe that our future CEOs should come from internal candidates whom the Berkshire board has grown to know well," he wrote.

Age will also be a factor, he suggested. Buffett is 84, while his second-in-command, Charlie Munger, is 91.

"Our directors also believe that an incoming CEO should be relatively young, so that he or she can have a long run in the job," he wrote.

Buffett said Berkshire will operate best if its CEOs average well over 10 years at the helm, noting: "It's hard to teach a new dog old tricks. And they are not likely to retire at 65 either - or have you noticed?"