Rashi on Numbers 26:4/רש"י על במדבר כ״ו:ד׳

1מבן עשרים שנה ומעלה כאשר צוה וגו׳ FROM TWENTY YEARS OLD AND ONWARDS, EVEN AS [THE LORD] HAS COMMANDED [MOSES AND THE CHILDREN OF ISRAEL, WHO CAME FORTH FROM EGYPT] that the counting of them (of those who came out from Egypt) should be from twenty years old and upwards, as it is said. (Exodus 30:14): “Every one that passeth amongst them that are numbered [shall be from twenty years old and upwards]”.