As a high school student in the 1970s, Lori Guess looked forward to packing up her oboe for a summer music camp in Sidney, Maine . The lakeside location and loon calls appealed to her, and it was a chance to connect with kindred spirits. Decades later, she’s still going to camp there. A separate band program was created for adults in 2013, where she felt encouraged to take up another instrument: trumpet. “I was thrilled because I love this place,” said Guess, 71, of Baltimore , a retired lawyer for the U.S. Department of Defense who plans to return to the New England Adult Music Camp in August. “It is serene, beautiful, a perfect setting.…