The first live philharmonic orchestra I saw was the Brooklyn Philharmonia, which is a smaller version of an orchestra. They played at an assembly in my high school and we were all pissed we were going to have to sit through an hour of torture. I guess I was like 13-14?
Well, these fucking people were geniuses. They did a cartoon themed show and the first song they played was the opening tune from Merry Melodies. That got everybody's attention. They then proceeded to play every song we had heard our whole lives from Bugs Bunny, Daffy Duck, Roadrunner, and every other cartoon from the 60's. it was an absolutely amazing show and got me started listening to classical music and orchestras. If you go to a concert hall and listen to them play without one electrical plug anywhere in site, it is just amazing sound.