How old was Aaron when he died?

Answer: 123

Aaron died on Mount Hor at age 123, in the fortieth year after Israel came out of Egypt.

“At the LORD’s command, Aaron the priest climbed Mount Hor and died there on the first day of the fifth month, in the fortieth year after the Israelites had come out of the land of Egypt. Aaron was 123 years old when he died on Mount Hor.”— Numbers 33:38-39 (BSB)