The James Levine Era has begun at Tanglewood, which has implications for more than just the Boston Symphony and its fans. Tanglewood is also home to one of the world’s preeminent orchestral training programs for young musicians, a program traditionally overseen by the BSO music director. So far, the center’s administrators and observers have raved about the maestro’s effect on the program, but privately, many of the young musicians have been saying that Levine’s baton technique can be vague and indecipherable. Still, there’s no doubt that Levine is shaking up Tanglewood, and has taken to the role of head mentor.