Thanks for posting this, great read. On March 2 I will hear Mahler 6 live at Boston Symphony Hall with the Boston Philharmonic Youth Orchestra. I'm excited.
You should be. I have listened to impressive performances from the Gustav Mahler Jugendorchester (an Austrian youth orchestra). https://en.wikipedia.org/wiki/Gustav_Mahler_Jugendorchester , they sometimes come to Lisbon.
They are surely top performers, selected from the best - and IMO the energy and emotional intensity of young orchestras brings us unique experiences.