John Gill Commentary Numbers 33:39

"And Aaron was a hundred and twenty and three years old when he died in mount Hor." — Numbers 33:39 (ASV)

And Aaron was one hundred and twenty three years old when he
died in Mount Hor .
] He was eighty three when he stood before Pharaoh, (Exodus 7:7) , and forty years he had been with Israel since, which make this number; he was three years older than Moses.