Last November he became the youngest ever player to represent the Blues when he came on against Luton in the FA Cup.
Duncan told BBC Essex: "Femi has got a fantastic opportunity, Everton are a big club, but it will all come down to how he approaches it from now on."
Duncan also revealed Orenuga, who joined the Shrimpers youth set-up when he was 14, had received a lot of interest from other Premier League and Championship clubs. But while he was sad to see him leave the Essex club for the north-west, Duncan said it would have been wrong not to let him go.
"It's a great opportunity for him and I don't think we should deny a young player the chance to play at a top level if it's right for the football club and good for the player. One thing we made sure of was that Femi was well aware of all the interest that was in for him, so that he had a clear mind and a clear option of where he wanted to go."