Conversation so far:
What did George M. Cohan do first?
George M. Cohan began his career as a child, performing with his parents and sister in a vaudeville act known as The Four Cohans.
How many skits did George M. Cohan write?
George M. Cohan began writing over 150 original skits and songs.
Who did George M. Cohan write these for?
George M. Cohan wrote them for the family act in both vaudeville and minstrel shows while in his teens.

Question: When did he write these?
Self-contained rewrite: When did George M. Cohan write over 150 original skits and songs in his early career?