Before the mountains were brought forth,To. That is the word that I am going to focus on in this verse. The word "to" stuck right between the "everlasting" and the other "everlasting". That little word to means 'as far as'.
or ever you had formed the earth and the world,
from everlasting to everlasting you are God.
Hold out your arm to the left. Now hold out your other arm to the right. Now stretch each one of them to infinity. That is how much God is God. From infinity as far as infinity, He is God.
In fact, He was God before your arms were made. Before there was a human to consider His God-ness, He was God. Before any of this matter or any of this energy, He was God.