What is a "matured" reef tank?

[squibege]

As a brand new reefer (first ever tank is just starting to cycle kind of new) it's intimidating to know that no matter how much I research and pre-plan... something's not going to go the way I want it to. I want nems and starfish and would love to have a Mandarin in my tank- but the arbitrary rule telling me to wait six months gives a reality check as to how much this hobby takes time and that rushing things will take a toll on the living things in your tank. The last thing I want to do is make a creature in my care suffer due to incompetence on my part, so I will wait the six long months until I add more sensitive things. No matter what I read I don't have a working knowledge on what a 'mature tank' looks/ acts like/has, so the six month rule is the easiest to go off of

Seasoned reefers at least know what rules are made to be broken