Quite simply ..the olden days.
The "Ancient of Days" refers to the Lord Jesus.
Dan:7:9: I beheld till the thrones were cast down, and the Ancient of days did sit, whose garment was white as snow, and the hair of his head like the pure wool: his throne was like the fiery flame, and his wheels as burning fire.
Dan:7:13: I saw in the night visions, and, behold, one like the Son of man came with the clouds of heaven, and came to the Ancient of days, and they brought him near before him.
Dan:7:22: Until the Ancient of days came, and judgment was given to the saints of the most High; and the time came that the saints possessed the kingdom.
