Simplify the following text for a Grade 7 native English-speaking person.
Original: At age 17 , Harding assembled a group of musicians to perform Pierrot Lunaire of Arnold Schoenberg , and sent a tape of the performance to Rattle in Birmingham .
Simplified: When he was 17 , Harding got together a group of musicians to perform Pierrot Lunaire by Arnold Schoenberg . He sent a tape of the performance to the conductor Simon Rattle in Birmingham .