WASHINGTON, Jan 30 (Reuters) - U.S. President Donald Trump on Friday said he will nominate former Federal Reserve governor Kevin Warsh to return as Fed Chair in May, as the president continues his campaign for lower U.S. interest rates. Here are five key things to know about Warsh: YOUNGEST-EVER FED GOVERNOR, CRISIS-TESTED Warsh, 55, ​joined the Fed Board of Governors in 2006 at age 35 as its youngest member after serving on former president George W. Bush's National Economic Council. He ‌remained at ...