Young joined the Watford academy system at 10 years of age. He developed there until the summer of 2001, when he was informed by the club that he wouldn't receive a full scholarship and could look for another team. Despite being turned away, Young stayed on at the club on a part-time basis and endeavoured to improve himself as a player and prove he could make it to the first team. He started to train with the Under-18s, despite being 16, and was starting games by the end of the season. He progressed on to the Under-21s and was eventually offered a professional deal by the club. The 18-year-old was handed his first-team debut under Ray Lewington in September 2003, scoring as a substitute against Millwall. He achieved five substitute appearances that season, scoring three goals, and made his first start for the club in the League Cup. Young came to prominence in the 2004–05 season, playing a part in 34 of Watford's league matches as they struggled to survive in the Championship. Although he failed to find the net, his performance during this season earned him the club's Young Player of the Season award.