By Ben Pound

GARY Rowett has challenged Millwall’s young guns to kick on and truly establish themselves in the first team next season after seeing Billy Mitchell sign a new long-term deal.Mitchell has made 23 appearances since making his first-team debut at the end of the 2018-19 campaign and was named the Lions’ young player of the year last season.The 20-year-old midfielder has made 12 outings this term since returning from a hamstring injury.Mitchell’s emergence into the first team has come alongside those of Danny McNamara and Tyler Burey and, with Hayden Mul...