When God sent Aaron to Moses (Exodus 4:14...), before they were to go back to Egypt to meet Pharaoh, had it been 40 years since Moses and Aaron had been together in each other's company?
Moses is Eighty years at the time of the Exodus:
(Exo 7:7 And Moses was fourscore years old, and Aaron fourscore and three years old, when >they spake unto Pharaoh.)
And he had to leave Egypt at the age of Forty:
Act 7:23-25 And when he was full forty years old, it came into his heart to visit his >brethren the children of Israel. (24) And seeing one of them suffer wrong, he defended >him, and avenged him that was oppressed, and smote the Egyptian: (25) For he supposed >his brethren would have understood how that God by his hand would deliver them: but they >understood not.
So he was out of Egypt forty years. Aaron being enslaved there, we might assume they did not meet those forty years until this verse:
Exo 4:27 And the LORD said to Aaron, Go into the wilderness to meet Moses. And he went, >and met him in the mount of God, and kissed him.
Aaron was three years old when Moses was born. To keep him alive, Moses was kept secretly at home for only three months before being placed in a basket and set adrift in the River Nile. He was found among the reeds by Pharaoh's daughter. Moses' sister arranged for their mother to nurse Moses, for which Pharaoh's daughter paid her. Later, "when the child grew older" he was adopted by Pharaoh's daughter.
In all probability, Moses was kept at home to be nursed until he was weaned but the Bible does not tell us if Aaron was at home during this time. Nothing is said about Aaron and Moses growing up together. All we are told is that Moses was adopted as the son of Pharaoh's daughter when he was a child (Exodus 2:1-10).
Acts 7:23-30 summarieses the events that unfolded. Moses was kept at home for three months. When Moses was 40 years old, he killed an Egyptian and had to flee for his life. He went to Midian, where he married, and he stayed there for 40 years. It was after his encounter with God in the burning bush that God arranged for Moses to return to Egypt and to meet Aaron in the desert.
When they first meet, prior to going to speak with Pharaoh, Moses was 80 years old and Aaron was 83:
Moses was eighty years old and Aaron eighty-three when they spoke to Pharaoh (Exodus 7:7).
I am unaware of any suggestion that while Moses was a member of the royal household he knew and spoke to his brother Aaron.