Complex sentence: Bailey spent two evenings a week plus many weekends away at camp with the Cadets, and at the age of about 17 years he became a sergeant-instructor and stayed in the Cadets for another 10 years.
Split into simpler sentences: Bailey spent two evenings a week plus many weekends away at camp with the cadets. At the age of about 17 years he became as sergeant instructor and stayed in the cadets for another 10 years.