From next season, he really needs to phase out Modric, and give Kroos some rest too.
Play Valverde, and give Blanco some chances(looked promising when he played).
But the problem is that his whole football is very dependent on players making the difference individually. There's a very basic and utilitarian system around that, so it's tough for Zidane to bring up youngsters. To develop a younger core you need better tactics because these players won't give you the individual quality right away needed for Zidane-ball.
You need a system that would fully incorporate fresh talent. Style-wise, Zidane is the wrong fit. It's much like the situation we were in with EV, except Zidane is the class version of EV. Still a wrong fit though.
Zidane is best if Madrid find ways to sign superstars. He'd be a top manager for players like Mbappe. If you give him good, but not incredible talent, he'll struggle to produce a top team imo.
Think of him like the reversed Klopp.