The most common and most likely answer to this crossword clue is the 5 plus 4 letter word SALAD DAYS
I've seen this crossword clue in The Guardian
S
A
L
A
D
D
A
Y
S
More clues leading to the result SALAD DAYS
- Prime commando unit outside city on June 6th
- Carefree youth with a woman trapping American lawyer on board a ship
- Fifties’ musical a beginner put on in States
- Talks about a son and daughter’s early years
- States welcoming star of Shane, the musical!
- Youth announces panto is to be held, but not at home
- Speaks about a son and daughter in musical
- Youth speaks about pantomime character dropping in
- Fondly-remembered youth’s healthy dishes covering twenty-four hours
- Speaks about a son and daughter making a musical
Buddy explains!

The straight part
We know that "Fifties’ musical" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case fifties’ musical = salad days.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.