Keeping up with the Beckhams! David Beckham and his wife, Victoria, proved they are one of the hottest celebrity couples during a recent boat day in Miami, Fla., with their son Cruz, 19, and the teenager’s 29-year-old girlfriend, Jackie Apostel. In photos obtained by OK!, the A-list couple could be seen boarding their $20 million yacht outside of their luxurious waterfront home last month. Dressed in a black dress with sunglasses on her head, Victoria, 50, showed off her muscular arms as she was assisted onto the lavish boat by a steward in a striped uniform shirt. Her husband, David, 49, was …