What is a mature plant in Cali?

In California, what constitutes a mature plant. I have gotten opinions from the day it starts to show an even minimal bud, to the day before it is ready to harvest. To have 12 immature and 6 mature plants, what you can grow differs greatly depending on what the definition is. Any legal eagles know for sure??? TIA

if your vegging, they are immature. if your flowering they are mature.