Born in Höchstadt, Grau joined the local athletics club &lt;a href="LSC%20H%C3%B6chstadt/Aisch"&gt;LSC Höchstadt/Aisch&lt;/a&gt;. His twin brother, Bastian Grau, also took up distance running. His international debut came at the age of eighteen, when he finished eleventh at the 2010 World Junior Championships in Athletics. He had his first international success at the 2011 European Athletics Junior Championships, where he was the steeplechase bronze medallist. He also ran in the junior race at the 2011 European Cross Country Championships that year, finishing 53rd.