Prince Josef Wenzel of Liechtenstein is 16 (born in May 1995). Infanta Elena of Spain’s son Felipe is 13 (born in July 1998). Crown Princess Mette-Marit’s oldest son Marius Hoiby is 15 (born in January 1997), but he isn’t titled. Lady Helen Taylor’s sons Columbus and Cassius are 17 and 15 (born August 1994 and December 1996), but they aren’t titled. Lady Sarah Chatto’s son Samuel is 15 (born in July 1996, but not titled. No one else is coming to mind right now.