מדרש אויף ויקרא 4:3

1) (Vayikra 4:3): ("If the anointed Cohein shall sin) to the guilt of the people.": The high-priest is being compared to the congregation. Just as the congregation brings (a sin-offering) only where (beth-din) erred (in the ruling), and they sinned unwittingly (on the basis of that ruling), so, the high-priest brings (a sin-offering) only where he erred (in ruling for himself) and he sinned unwittingly (on the basis of that ruling)(Why the inclusion clause for the high-priest?) Does it not follow naturally? viz.: The congregation is distinct from the individual (in its offering), and the high-priest is distinct from the individual. Just as the congregation brings (a sin-offering) upon error in ruling and deed-unwittingness, so, the high-priest.

1) (Vayikra 4:3): ("then he shall offer a) bullock." I might think (he could offer) even an old one; it is, therefore, written "ben" (connoting a young one.) If "ben" alone were written, I might think it meant a very young one (i.e., one or two years old); it is, therefore, written "bullock. What satisfies this? A three-year-old. These are the words of R. Meir. The sages say: Four and five-year olds are also kasher, but old ones are not brought, out of deference (to the L–rd).

2) — But why not go in this direction? The nassi is distinct from the individual, and the high-priest is distinct from the individual. Just as the nassi brings (a sin-offering) for deed-unwittingness (alone, without an error in ruling), so, the high-priest!