Conversation so far:
How old was Stan Kenton when he started his career?
Stan Kenton was 25 when he would make his first recordings when Arnheim made 14 sides for the Brunswick label in summer of 1937.
Was Stan Kenton immediately successful?
Stan Kenton wasn't immediately successful, but he was very talented from a young age.
Where did Stan Kenton begin his career?
Stan Kenton was 25 when he would make his first recordings when Arnheim made 14 sides for the Brunswick label in summer of 1937.

Question: What did he start out doing in his career?
Self-contained rewrite: What did Stan Kenton start out doing in his career?