Aaron was 123 years old when he died on Mount Hor.
39. And Aaron was an hundred and twenty and three years old. It is not without reason that the great age of Aaron is expressly stated, inasmuch as his life had been prolonged to an unusual period, for the good of the people.
And the Lord spake unto Moses in the plains of Moab by Jordan, near Jericho,.... See Gill on Num 33:48; see Gill on Num 22:1, saying; as follows.
FROM SINAI TO KADESH AND PLAINS OF MOAB. (Num. 33:16-56) Kibroth-Hattaavah ("the graves of lust," see on Num 11:34) --The route, on breaking up the encampment at Sinai, led down Wady Sheikh; then crossing Jebel-et-Tih, which intersected the peninsula, they descended into Wady Zalaka, pitching successively at two brief, though memorable, stations (Deu 9:22); then they encamped at Hazeroth ("unwalled villages"), supposed to be at Ain-Hadera (see on Num 11:35).
Commenting on Numbers 33:16-56