We read more often in the Bible that the age of people is mentioned at important times in their lives: for example, of Abram/Abraham in Genesis 12:4; Genesis 16:16; Genesis 17:1, Genesis 17:24; Genesis 21:5.
We are told the age of Moses in Acts 7:23 (40 years); here in Exodus 7:7 he is 80 years, and in Deuteronomy 34:7 when he dies (at 120 years). Moses’ life can be divided into three periods of 40 years each, of him being prince, shepherd, and leader.
Aaron is the oldest son of Amram and Jochebed; Moses is his younger brother. However, the younger brother has a more important position than his older brother, a theme that also appears regularly in the patriarchs: Isaac is greater than Ishmael (Genesis 17:19–21), Jacob is greater than Esau (Genesis 25:23), and Ephraim is greater than Manasseh (Genesis 48:17–19).
Aaron also, the firstborn son, is in service to his younger brother Moses. Aaron obeys, as we do not read anything about jealousy or protest, except later, just once, in Numbers 12:1–16.
7 Now Moses was eighty years old, and Aaron eighty-three years old, when they spoke to Pharaoh.