6. Callum Watson – London Irish (17 years, 311 days)
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Probably the least well known of the Watson brothers (Anthony and Marcus), Callum initially made his debut for the Exiles in 2014. The scrum-half is now playing for Loughborough Students in National League One.
5. George Ford – Leicester Tigers (17 years, 256 days)
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He became the youngest Rugby Union player to make his professional debut in England at just 16 years and 237 days old when Leicester played Leeds in the LV= Cup. His Premiership debut didn’t come until later.
Ford has since developed into a fine fly-half, winning 37 caps for England thus far. The 24-year-old did leave Tigers for a while to join his father, Mike at Bath but returned to Welford Road in the summer.
4. Ben Youngs – Leicester Tigers (17 years, 231 days)
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Son of former scrum-half Nick and brother to club captain Tom, Leicester Tigers is in the blood of scrum-half Ben Youngs.
An academy graduate, he became the club’s youngest-ever league player when he ran out for his debut in a match at Bristol in April 2007 and came off the bench in 2006/07 Premiership Final win over Gloucester before his 18th birthday.
He’s since represented a British & Irish Lion in Australia in 2013 and has established himself as England’s first choice scrum-half ahead of countryman Danny Care.