Tosefta for Parah 1:3
כְּבָשִׂים, בְּנֵי שָׁנָה. וְאֵילִים, בְּנֵי שְׁתַּיִם. וְכֻלָּם מִיּוֹם לְיוֹם. בֶּן שְׁלשָׁה עָשָׂר חֹדֶשׁ אֵינוֹ כָשֵׁר לֹא לְאַיִל וְלֹא לְכֶבֶשׂ. רַבִּי טַרְפוֹן קוֹרֵהוּ פַּלְגָּס. בֶּן עַזַּאי קוֹרֵהוּ נוֹקֵד. רַבִּי יִשְׁמָעֵאל קוֹרֵהוּ פַּרְכָדִיגְמָא. הִקְרִיבוֹ, מֵבִיא עָלָיו נִסְכֵּי אַיִל, וְלֹא עָלָה לוֹ מִזִּבְחוֹ. בֶּן שְׁלשָׁה עָשָׂר חֹדֶשׁ וְיוֹם אֶחָד, הֲרֵי זֶה אָיִל:
Sheep [as referred to in the Torah] are one year old. And Rams [refers to ones who] are two years old. And all of them [are counted] from day to day [i.e. their years are counted from the day of their birth]. At thirteen months old niether a ram nor a sheep is valid [as a sacrifice]. R' Tarfon called it a "pleg'es." Ben Azzai called it a "nokad." R' Yishmael called it a "parchadigma." If it was offered, they bring with it wine libations of a ram and it doesn't count to the alter [i.e. to fulfill any obligations]. At thirteen months and one day it is considered a ram.