#3 Ryan Giggs (17 years, 5 months and 5 days)
Ryan Giggs is a household name for Manchester United and Premier League fans all over the world. The Welshman graduated from Manchester United's academy and made his debut on March 2nd 1991 in a 2-0 defeat at the hands of Everton. Sir Alex Ferguson was the manager who handed Giggs his debut for the club.
Despite already having made his first-team bow, Giggs remained captain of the youth team and led them to FA Youth Cup glory in 1992. The team consisted of a number of future Red Devils stars, including David Beckham, Paul Scholes, Nicky Butt, Gary Neville and Phil Neville. Giggs scored his first goal for the club in a 1-0 win over Manchester City on May 4th 1991 aged 17 years, five months and five days.
Giggs spent his entire career at Manchester United until his retirement in 2014 in a glittering career in which he won everything. On the day of his retirement, he was appointed as the club's assistant manager. He went on to manage the club briefly on an interim basis before taking the manager's job of the Wales national team. Giggs remains the most decorated player in Premier League history.
#2 Sammy McIlroy (17 years, 3 months and 4 days)
Sammy McIlroy joined the Manchester United youth set-up in 1969 before signing his first professional contract with the club when he turned 17 in August 1971. He made his debut for the club in a 3-3 draw against Manchester City in November 1971.
McIlroy marked his debut appearance for the club with a goal, when he scored the game's first in the 39th minute of the clash. The Northern Irishman spent the first 11 years of his career at Old Trafford before securing a transfer to Stoke City in 1982 for a then club-record £350,000.
McIlroy is remembered for being Sir Matt Busby's final signing at Old Trafford. He won the FA Cup in his time at the club and made 419 appearances in total, scoring 71 goals.
#1 Norman Whiteside (17 years and 8 days)
Norman Whiteside remains the youngest player ever to score a goal for Manchester United. The Northern Irishman joined the club as a 16-year-old and made his debut about two weeks before his 17th birthday against Brighton and Hove Albion.
Whiteside scored his first goal for the club in a 2-0 win against Stoke City on 15th May 1982, eight days after he turned 17 years old. The midfielder spent eight years at Old Trafford before moving to Everton in 1989 for a fee of £750,000.
In addition to this record, Whiteside is also the youngest player to participate in the FIFA World Cup, and the youngest to score in the FA and League Cup finals. Whiteside retired two years after his move to Everton due to a knee injury that he had first suffered in July 1981.