Jamieson, Fausset and Brown on Genesis 9:24

24. This incident could scarcely have happened till twenty years after the flood; for Canaan, whose conduct was more offensive than that even of his father, was not born till after that event. It is probable that there is a long interval included between these verses and that this prophecy, like that of Jacob on his sons, was not uttered till near the close of Noah's life when the prophetic spirit came upon him; this presumption is strengthened by the mention of his death immediately after.