<p>You might want to look at Kendall Betts Horn Camp, though it will have horn choirs but no orchestra. KBHC takes a limited number of high schoolers and I think requirements are to have finished eighth grade AND be 14, however you could email and see what they say. Our D went for the first time at 15 and was one of the youngest, but fit in fine. Most of attendees are college/graduate/adult.</p>