The Aston Villa winger hopes to complete his move to United in the coming days.
Young continued his school education into his late teens while training twice a week with Watford, before Ray Lewington handed him a professional contract at the age of 18.
By that stage, Lewington knew he had one of the best British talents in a generation.
He told the People: "I remember watching one of the kids' games one day, and I asked about him.
"Dave Dodds, who was in charge of them, told me: 'That's Ashley Young, and I think he is going to play for England.'
"Doddy's not prone to exaggeration, and then reserve team manager Nigel Gibbs told me the same.
"I have to admit I wasn't so sure ... it didn't take long to convince me, though.
"Exciting players like him rarely come along. He could use both feet, and defenders couldn't deal with him.
"To be honest, I think one of the reasons he didn't get a scholarship might have been that his parents wanted him to continue his education, just in case.
"They were brilliant at dealing with him and prepared him for what was to come."