Allah is not created because He is not a creation. He is the creator of all the creations as we see before. He just says "Be" and it is. Only because we are creations, we thought that Allah should be created as us. But the first meaning of is He shouldn't be created because if He'd been created, there should have been a creator for Him. At this moment, it would not be God.
Moreover, Prophet Muhammad (PBUH) describes God in one Hadith, saying:
You are the First, for there is nothing above You, and You are the Last, for there is nothing after you. And you are az-Zahir, for there is nothing above you. And you are Al-Batin, for there is nothing below You." (5)
The same meaning is mentioned in Qur'an:
He is the First and the Last, the Ascendant and the Intimate, and He is, of all things, Knowing." (6)