Joe Gomez was available. You stated that no manager would choose a youth prospect over an experienced player (I'm paraphrasing there).
Indeed, but Ferguson was played until he stopped bagging them. Point stands, he was a youth player given his shot.
You're not too familiar with coaches and coaching then, that's precisely how they think.
Oscar Bobb, James McAtee, Wilson Esbrand. Foden was included in the squad in 2016, Palmer was given a shot. Exceptionally talented, but all given a taste of first team Football with an eye to the future.
Far too simplistic. Youth players may get their shots a little earlier than expected, should injury force the Coaches hand, but they're brought into the squad in the first place to integrate them and give them a feel for first team Football. They're literally doing that with a view to the future. Some have more luxury to do it than others, but all do it to greater or lesser extents.