If God existed eternally, then why did he decide to create the universe only 13.7 billion years ago?
This is actually a wonderful question, one which philosophers, including medieval Muslim philosophers have pondered on.
There are a number of things we must consider: How do we define 'time'? Does time itself have a beginning? Does an eternal being have to exist in eternal past time and future time?
Firstly, there are two ways i believe for an eternal being to exist. One is eternal within time, whereby this being exist infinitely in time - past and present , which presents a lot of philosophical problems.
The second is to transcend time and space, and exist outside of time and space - which is what we muslims believe in.
Therefore 'time' itself 'began' when God created it, and there was no 'deliberation' or 'an hour' before time where God began to ponder upon creation.
So arguing why Allah swt did not create 'sooner' is irrelevant - there was no 'sooner'. If you believe this you then limit Allah swt to time and sequential events, and ascribe partners to him - namely time and Allah swt co-eternally existing in my view.
I cite the following Hadith:
He said: A man came to Abu’l Hasan ar-Rida عليه السلام from beyond the Balkh river and said: I will ask you a question, if your answer to me is the same as that which is with me [I will accept your cause]. So Abu’l Hasan عليه السلام said: Ask whatever you wish. So he said: Inform me about your Lord, when did He come into being? And how is His state? And upon what thing does He rely? So Abu’l Hasan عليه السلام said: Allah تبارك وتعالى was there before there was a “there”, and He was being before there was a “how”, and His reliance is upon His power. .....al-Kafi, Volume 1, hadith 233) Graded SAHIH by Alama Majlisi
The hadith states that God was there before a 'there' and in being before 'how'. Therefore there are no sequential events leading to God, nor are there even concepts of mechanisms. 'There' and 'How' are concepts created by God.
This is why Allah swt cannot move. If he moves from point x to point y, he is acting within time. It totally wreaks philosophical havoc into proving his existence.
God also does not 'exist' in space or a location with coordinates, therefore can not 'move'.