"Mature tank" seems to be in the eye of the beholder. When I set up my 10 gal. I used everything out of a larger established tank. It still took about 3 months to completely cycle and now at 12 months it's just becoming what I would call mature. It is now consistantly stable, the corals are taking off and coraline algea is beginning to spread. Another thing to keep in mind is the inherent instability of small tanks. Because of this it almost seems to take them longer to mature than a larger one.
Ken