Aaron born
Aaron, son of Amram and Jochebed of the tribe of Levi, was born three years before Moses.
Amram took Jochebed his father’s sister to himself as wife; and she bore him Aaron and Moses. The years of the life of Amram were one hundred thirty-seven years.
Exodus 6:20 (World English Bible)
Aaron would become Moses' spokesman before Pharaoh and Israel's first high priest. Their sister Miriam was older than both.
Dating notes
Aaron was 83 when he and Moses spoke to Pharaoh (Exodus 7:7).