שמות ז:ז פירוש: ספורנו, אור החיים וטור הארוך

ומשה בן שמונים שנה, even though he was an aged man both he and his brother rose early in the morning to do their Creator’s bidding. Although some people lived to a ripe old age in those days, eighty was an age which was considered as very much part of what we call “old age.” We know from David in Psalms 90,10 that reaching the age of 80 was considered an exceptional feat, i.e. kindness of G’d.

בדברם אל פרעה, when they spoke to Pharaoh. The word בדברם refers to the first day Moses and Aaron spoke to Pharaoh. They were certainly somewhat older as time went on.

ומשה בן שמונים שנה, “and Moses was eighty years old, etc.” Ibn Ezra, in dealing with the age of Moses at this time, mentions that no other prophet has ever been described as practicing his prophecy at such an age. The only ones able to do so were those that enjoyed an exceptionally high level of prophecy,