ANSWER: Your question about what is the Glory of God is a beautiful truth about our heavenly Father. Most people in the world, as well as many Christians, think of Him as someone who is old when they wonder what he looks like.
When we humans are born, we are in a most healthy or incorruptible state. From that point on, we grow to maturity and then decay or corruption sets in until we get old and die. Only the physical creation, including humans, get old (1Corinthians 15:42). The apostle Paul, when asked what kind of body God will give those in the resurrection, gave the following comparison.
40. And there are heavenly bodies, and earthly bodies; but the glory of the heavenly is different, and the glory of the earthly is different. 42. So also is the resurrection of the dead. It is sown in corruption; it is raised in incorruption.
49. And as we have borne the image of the one made of dust, we shall also bear the image of the heavenly one (1Corinthians 15:40, 42, 49, HBFV throughout)
Notice, we humans are born in dishonor (corruptible) but in the resurrection, we will be incorruptible. The Apostle Paul states earthly bodies (terrestrial) have a glory but are corruptible. Celestial bodies like the stars have a different kind that is beautiful and age lasting. Then in 1Corinthians 15:48 - 49, Paul said we are going to have the image (likeness) of the heavenly or the Man from heaven, which is likely a reference to Jesus Christ. Therefore, when the Bible speaks of glory, it refers to how a being or a person appears. Since Paul tells us we are going to look like the 'heavenly one,' it is a beautiful truth to see how our Father looks.
Psalm 104:1 - 2 states the Eternal's garment is light and in Psalm 27:4, David writes He is beautiful. In Revelation 4 and many other scriptures, we see He is so beautiful to look upon that He is like beholding every precious gem there is with the entire spectrum of the rainbow. In fact, round about His throne, there is a rainbow (Revelation 1, 4). Since white is what He is clothed with and white is the containment of the entire color spectrum, he changes His brilliance and Glory as He chooses. In Revelation the first chapter, it says his eyes are a flame of fire.
God is the source of all life or energy. His Glory is perpetual energy or self-producing energy that radiates all the beauty of the color spectrum as a glorious jewel. It represents, besides His unfathomable beauty, His unlimited power (complete energy), His righteousness, perfection, holiness, goodness, and unending love. In Revelation 21, the bride of Christ, which is New Jerusalem, contains twenty different gems besides gold.
In Daniel 7:9, the Almighty is known as the Ancient of Days (always existed) but this does not mean he looks old. He does not want us to make an image of Him because His majesty is so awesome it would only be a counterfeit. This is the glory of God. May we love and praise Him for what he is.