English Explanation of Mishnah Parah
Lambs no more than one year old, And rams no more than two years old. When the Torah mandates bringing a lamb-offering, it must be within its first year. This is explicit in the Torah, see for instance Numbers 7:17. Rams adult sheep must be at least within their second year.
Rashi
למטה יהודה [NACHSHON THE SON OF AMINADAB,] OF THE TRIBE OF JUDAH — By these words Scripture merely states his genealogy after his tribe, and they do not mean that he collected the offerings from his tribe and offered them on their behalf. Or perhaps it does state למטה יהודה only to intimate that he collected the offerings from his tribe and then brought them? Scripture, however, states, (v. 17): this was the offering of Nachshon — he brought it of that which was his own (Sifrei Bamidbar 48).
Rav Hirsch
V. 14. חלב כרים .חמאת וגו׳ wie חלב כליות חטה Ausdruck für das Fetteste und Beste. כרים, die Etymologie von כר ist dunkel. Vielleicht sind כרים von Schafen, was עתודים von Ziegen. עתודים siehe Bamidbar 7, 17. כליות חטה die einzelnen Körner einer Ähre werden an Größe mit den einzelnen Teilen einer Niere verglichen.