what are 'salad days' ? What does 'coming of age' mean?

“Salad Days” was the title of a British musical in the 1950s or 60s. Think it was about a bunch of privileged English kids leaving the playground of university and facing the harsh reality the real world where finding a job typically meant going to see an uncle who worked in high places. Might need a bit of work to adapt for 21st century audiences. Then again maybe not, privilege never dies.