Frédéric Arnault, the 26-year-old chief executive of TAG Heuer, may be the youngest CEO of a luxury watch brand in the world. Like his half-siblings from his father’s first marriage, Antoine (chief executive of Berluti, head of image and environment for the group, member of the LVMH board) and Delphine (executive vice president at Louis Vuitton, member of the LVMH board) and his older brother, Alexandre (executive vice president for product and communications at Tiffany) and