The Hamilton kid, who turned 14 just over a week ago, agreed to join the Hoops despite a 90-minute face-to-face chat with guvnor Fergie.
Hill told the Scottish Sun: "I'm happy to get it all sorted. It's been a busy summer. I went down to Carrington which was brilliant. I met Alex Ferguson at a hotel which was fantastic, although my mum was more excited than me!
"She's always been a United fan. When he came in she was like 'It's a pleasure to meet you Sir Alex'. I was just sitting there.
"After meeting him and seeing Carrington, it was very hard to say no. We got advice on our options from the agents at Viola FC, but my family left the final decision to me.
"I felt Celtic was the better move at this time of my life."