After three years in Aachen's academy, Holtby signed a professional contract with the club during the 2007–08 season. He was then handed his first-team debut at the age of 17 by caretaker manager Jörg Schmadtke in December 2007, coming on as a second half substitute for Mirko Casper in a 2–2 draw with FC St. Pauli. His debut was one of only two appearances for the season, with his second coming in a 3–1 loss to TuS Koblenz on the last match day of the campaign. The following season, Holtby was converted to the left wing position by new club manager Jürgen Seeberger. Excelling in his new role, he scored his first goal for the club on 8 December 2008 against 1860 Munich before netting a brace in a 6–2 drubbing of Nürnberg in February the following year. He ultimately made 31 appearances for the season and scored eight goals as Aachen ended the campaign in fourth place, narrowly missing out on a spot in the promotion playoffs. Holtby's form for the season saw him awarded the Gold Fritz Walter Medal for the best German U19 player in 2009, ahead of runners-up Konstantin Rausch and André Schürrle.