Sforno on Numbers 1:45/ספורנו על במדבר א׳:מ״ה

1ויהיו כל פקודי....כל יוצאי בישראל צבא, none were over sixty years of age, as people of that age and beyond were not allowed to go out to war. We know this from Baba Batra 121 concerning Yair ben Menashe and others included in the count mentioned there. The decree that the generation of the spies would have to die in the desert applied only to the ones between 20-60. Those younger or older at the time of the spies’ trip were exempt from this decree.