If you’ve already had your “moment in the sun” it means that you’ve already experienced your best times. This is a common phrase and can be applied in many situations. It means “your best days are in the past”.Here are 2 fantastic examples:
The US economy might continue to get worse and worse because of international competition. I think they’ve already had their moment in the sun.
Britney Spears has already had her moment in the sun. She will never again be as famous as she was 10 years ago.
Britney Spears has already had her moment in the sun. She will never again be as famous as she was 10 years ago.
I think you get the idea. Your “moment in the sun” is your best time. If you’ve already had your “moment in the sun” your best days are “behind you”