Background: Thomas Simpson (30 November 1937 - 13 July 1967) was one of Britain's most successful professional cyclists. He was born in Haswell, County Durham and later moved to Harworth, Nottinghamshire. Simpson began road cycling as a teenager before taking up track cycling, specialising in pursuit races. He won a bronze medal for track cycling at the 1956 Summer Olympics and a silver at the 1958 British Empire and Commonwealth Games.
Context: Simpson was born on 30 November 1937 in Haswell, County Durham, the youngest of six children of coal miner Tom Simpson and his wife Alice (nee Cheetham). His father had been a semi-professional sprinter in athletics. The family lived modestly in a small terraced house until 1943, when his parents took charge of the village's working men's club and lived above it. In 1950 the Simpsons moved to Harworth on the Nottinghamshire-Yorkshire border, where young Simpson's maternal aunt lived; new coalfields were opening, with employment opportunities for him and older brother Harry, by now, the only children left at home. Simpson rode his first bike, his brother-in-law's, at age 12, sharing it with Harry and two cousins for time trials around Harworth. Following Harry, Tom joined Harworth & District CC (Cycling Club) aged 13. He delivered groceries in the Bassetlaw district by bicycle and traded with a customer for a better road bike. He was often left behind in club races; members of his cycling club nicknamed him "four-stone Coppi", after Italian rider Fausto Coppi, due to his slim physique.  Simpson began winning club time trials, but sensed resentment of his boasting from senior members. He left Harworth & District and joined Rotherham's Scala Wheelers at the end of 1954. Simpson's first road race was as a junior at the Forest Recreation Ground in Nottingham. After leaving school he was an apprentice draughtsman at an engineering company in Retford, using the 10 mi (16.1 km) commute by bike as training. He placed well in half mile races on grass and cement, but decided to concentrate on road racing. In May 1955 Simpson won the National Cyclists' Union South Yorkshire individual pursuit track event as a junior; the same year, he won the British League of Racing Cyclists (BLRC) junior hill climb championship and placed third in the senior event.  Simpson immersed himself in the world of cycling, writing letters asking for advice. Naturalised Austrian rider George Berger responded, travelling from London to Harworth to help him with his riding position. In late 1955, Simpson ran a red light in a race and was suspended from racing for six months by the BLRC. During his suspension he dabbled in motorcycle trials, nearly quitting cycling but unable to afford a new motorcycle necessary for progress in the sport.
Question: When did he start club racing?

Answer:
Tom joined Harworth & District CC (Cycling Club) aged 13.