WASHINGTON, Jan 16 (Reuters) - At 72, U.S. Federal Reserve Chair Jerome Powell has grandkids to play with, a golf game to get back to and a tune or two to master on the guitar. He also faces a choice: Whether to devote the next years to his family and passions or to battling from inside the Fed to shape if not stymie any Trump administration effort to undermine the independence of the world’s most important central bank or radically remake its structure. Though his term as Fed chief ends in May,