By youth he means youth academy, I understand the problems with chelsea, lets be honest here our youth prospects at the time were crap, we'd come up with one good player of a chelsea mainstay quality every ten years. He did fairly well with porto however. Carvalho being the main example, he also promoted bosingwa too and had a fairly young squad.
With inter he did use balotelli quite a bit, in fact balotelli has had the most appearances in a season under jose mourinho than any other manager.
He could have kept bonucci but tbh he was part of the milito deal. He was also able to promote santon.
However the problem has never been him not being able to use a young squad. Real madrid are a testiment to that, di maria, ozil, khedira, marcelo, benzema were crucial parts of the team. The problem has been promoting players from the youth academy directly, but if we look at most managers and teams, the only teams who have done that very successfully recently from academy players have been bayern, barcelona and AC milan, arsenal too to an extent recently(not in the early wenger era though as buying a load of french players for cheap in a golden age of french football is nothing major, people do the same thing with germany now) but its a very hard job to do.
If we look at youth academy players/people who have come through castilla he's used, Callejon, granero and morata are the first 3 that come to mind, jese rodriguez and nacho as well in fact nacho even got a decent run in the team last season. I think he made a mistake in selling dani carvajal as he could have been useful this season at right back instead of putting essien there but real are getting him back anyway.
I'd say that mourinho has done what he could with the youth.