Actually got me thinking as well. First thought was that Moyes was the one to sign Stones, but all he did in the 6 months before he left was put him on the bench a few times. He was around 18-19 then. Also remember he chased after Kyle Walker (and the other Kyle that was more highly rated, they both signed for Spurs that summer).
Baines and Coleman were like 21 and 22 respectively when he handed them their first EFC games, and both were actually played quite early on after signing. They also had ample experience from before.
Not counting other things like the Europa League dead rubbers where he fielded a squad of schoolboys, or other anomalies like Jack Rodwell (debut age 16 in midfield, could technically play and occasionally, much later, played centre back)... I can't think of a youngster getting a debut in defence
Moyes record with blooding youngsters used to be very aggressive. It feels like it has changed. Might be the game has changed a bit anyway.
Anyway, my impression is that getting them ready in terms of mentality or physicality is what's going on with Aznou and Dibling. Though that would only be speculation.