The Ancient of days is the awareness of being, the I AM, older than every thought and every figure that will ever pass through you. It is not an old man on a distant throne but the oldest thing in you, the sense that you exist, which fathered everything you have ever imagined. The thrones cast down are the fixed positions from which you once ruled your life, the settled opinions about who you are and what you can be, dropping away so the original power can take the seat.
White garment and white hair carry no age here; they mean the wearer is spotless, unstained by anything that ever happened to him. Fire is the creative energy of imagination, and the throne and the turning wheels burn because this power is never still and never cools. What sits down when your old positions collapse is your own consciousness, awake at last, running the whole scene from within you.