To whom does "Tedaber" refer?
Ramban #1, Moshav Zekenim #1: Moshe was instructing Aharon, the one who was in charge of Korbanos, to instruct the people what they must bring, in order to boost his esteem in the eyes of the people.
Ramban #2, Moshav Zekenim #2 : Moshe instructed Aharon and the elders (mentioned in Pasuk 1) to instruct the people what they must bring.
Ramban #3: Moshe instructed Aharon to take the prescribed Korbanos for himself and the elders (mentioned in Pasuk 1) to instruct the people what they must bring.
How old is an 'Egel'?
Rashi (on Pasuk 7): An Egel is in its first year. We learn from here to everywhere.
Rashi (verse 7) writes that we learn from here that an Egel is a yearling. We say about testimony that "Ed" is always two, unless the Torah specifies one. Also here, we should say that Egel is in its second year, unless it says "Ben Shanah"!
Riva: We cannot say so, for Egel does not imply Ben Shetayim more than Ben Shanah. Ed implies two, for [normally] testimony is not less than two. 1
We know this from elsewhere, e.g. "Al Pi Shnei Edim
Rashi (verse 7) writes that we learn from here that an Egel is a yearling. If so, we should similarly about Keves. Why did the Torah write 51 times about Kevasim 'Ben Shanah'?
Perhaps these are 51 Kesuvim ha'Ba'im k'Echad. The only 'Kevasim' written about Korbanos where it does not specify a yearling are Chatas 1 , the male lambs of a Metzora 2 , and Nesachim 3 (4:32, 14:10, 21, Bamidbar 15:5). (PF) Meshech Chachmah (5:6) - Parah 1:3 teaches that Keves is always a yearling 4 . Kesev includes older animals, e.g. Olah, Shelamim, the Isur of Chelev, Shechutei Chutz, Ba'al Mum and the Heter to eat them (1:10, 3:7, 7:23, 17:3, 22:19, Devarim 14:4). Sometimes Chata'os are called Kesev (4:35, 5:6) even though they are yearlings.
The Torah specified that a goat Chatas for idolatry must be a yearling (Bamidbar 15:27). "Torah Achas Yihyeh Lachem" (ibid., 29) teaches that the same applies to all Chata'os (Sifra, Chovah 7:10:2. Malbim (283) - we need not learn to Kesavim, for the Torah always says "Benei Shanah", and after a year it is called a ram. Rashi (Kidushin 55b) - every Kisbah is a yearling. (Refer to 9:3:153:1***.)
Perhaps we learn from a Metzora's Kivsah; the same verse calls it a yearling. However, if so, we could learn also "Temimim" from the Kivsah; why did the Torah write Temimus about both of them? (PF)
The Torah specified Nesachim for Kevasim and rams. In Menachos (91b), Bar Pada was unsure what is the Nesech for a Palgas (a sheep in its 13th month; perhaps it is included in Keves). R. Yochanan holds that it is a new entity, and "Oh la'Ayil" teaches about it. (Surely, he holds that after 12 months it is not called Keves! - PF)
Also Tiferes Yisrael there says so. The Rishonim did not say so; they could explain the Mishnah to teach that whenever Keves must be a yearling, this is from day to day. (PF)