If something has matured, it has grown and developed fully.
Matured things are usually good and ready to be used or enjoyed.
Examples:
The fruit has matured and is ready to eat.
The wine has matured for many years.
The cheese has matured and tastes delicious.
My little brother thinks he has matured, but he still acts like a baby sometimes.
The plan has matured and is now perfect.
The idea matured in my mind and became a great invention.