במדבר ח:ח מקורות במשנה: Mishnah Parah

Rabbi Yose the Galilean said: bulls must be no more than two years old, for it is said, "And the second bull you shall take for a sin-offering" (Numbers 8:8). But the sages say: they may be even three years old. Rabbi Meir says: even those that are four or five years old are valid, but old animals are not brought out of respect.