His career at this young age ended because his mother wanted her son to have a real childhood. As an adult, his first job in films was as a co-writer of the 1939 Ronald Reagan movie Code of the Secret Service.
The passage describes how a person's early career ended due to their mother's desire for them to have a normal childhood. Later, they entered the film industry as a writer on the movie "Code of the Secret Service," which starred Ronald Reagan.