Everyone needs to calm down! He's got obvious potential, and maybe he should be given a few more sub appearances but he's nowhere near ready to be a starter.
He's still too raw, capable of moments of brilliance but as seen tonight he was also impulsive and tactically naive at times.
Starting him only to have him underperform will harm his development, Allegri clearly likes him and rates him, and will give him games when he's ready. He gave De Sciglio and El Shaarawy chances at Milan, he's not afraid to play youngsters!