In the present now, many clubs are beginning to look into prioritizing young players over older players who would make up their team squad for long term purposes. Manchester United choosing to go in that area(more young players) is not a bad idea because it is much better to have a coach who will use his hands to groom the players to the formation he wants, over time they will fit into the position he wants them to be, instead of having older players who would keep messing up without showing good results in the pitch. However, all these would take time before the results would manifest, I believe Manchester United management and fans would trust the process rather than being in a hurry to call for the sack of Amorim when the young players haven't mastered each other playing patterns
The truth is that when a club is trying to build their team that'll last for over 6 years, they usually go for young players who are talented to achieve that. Looking at the current Manchester United squad, I think they have a missed set of young and veteran players but if you're talking about their future signings, I think the new manager will want to sign younger players that he'll want to build his team around.
Ruben Amorim I think have the experience that's sufficient enough to build a young team into a world class team so with the backing of the club's management, he'll surely achieve his aims.