God has always existed. He created the universe and everything in it. He exists outside of time itself. All of creation, from the beginning of the universe to its end, is one eternal “right now” to God.
God has no physical form aside from the humanity taken by Jesus. The Father and the Holy Spirit are wholly spirit. God can appear to mortals in the guise of a physical form (such as the Holy Spirit descending as a dove at Christ’s baptism) though. When God appears to man it is known as theophany.