If Mourinho was asked to give youth a chance, he might. Real Madrid and Chelsea don't care about giving youth a chance, it's not a part of those club's, he had no reason to give youth a chance. At Inter, he actually spoke of bringing youth through, Balotelli's first full season was under Mourinho, Santon was another, others were given chances too. At Inter: “the most important part of my job at the moment is the improvement of the youth here. They have big potential and I think I have the conditions to help improve them."
At the start of his 2nd spell with Chelsea he said “If you don't bring kids through the academy, the best thing is to close the academy”, he chose against loaning out Loftus-Cheek this season as he felt he was ready, with Chelsea struggling though maybe found it hard to give him more chances.
There's no guarantee he would give chances to youth but he knows what United's about, he's not new to football, he knows the history. I think he really wants the job and will do what's asked of him.